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SCIENCES 

LIBRARY 


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SOME  PHASES  OF 

THE  PLEISTOCENE 

OF  IOWA 


BY  EMMETT  J.  fcABLE 


JGAl 


BERKELEY 


UNIVERSITY  OF 
CALIFORNIA 


EARTH 

SC/ENCES 
LIBRARY 


EXCHANGE 


THE  UNIVERSITY  OF  IOWA 

SOME  PHASES  OF 

THE  PLEISTOCENE 

OF  IOWA 


WITH    SPECIAL    REFERENCE    TO    THE    PEORIAN 
INTERGLACIAL  EPOCH 


A  DISSERTATION 

SUBMITTED  TO  THE  FACULTY  OF  THE 
GRADUATE  COLLEGE  IN  CANDIDACY 
FOR  THE  DEGREE  OF  DOCTOR  OF 
PHILOSOPHY  DEPARTMENT  OF  GEOLOGY 

BY  EMMETT  J.  CABLE 


EARTH 

SCIENCES 

LIBRARY 


CONTENTS. 


INTRODUCTION. 

CHAPTER  I.       THE  HISTORY  OF  INVESTIGATION  AND  CLASS- 
IFICATION OF  THE  PLEISTOCENE  OF  IOWA. 
CHAPTER  II.      THE  DRIFT  SHEETS  OF  IOWA. 
CHAPTER  III.    THE  INTERGLACIAL  DEPOSITS  OF  IOWA. 
CHAPTER  IV.    THE  LOESS. 
CHAPTER  V.      THE  PEORIAN  INTERGLACIAL  EPOCH. 


INTRODUCTION. 

Purpose  of  this  report. 
Preliminary   preparation. 
Area   of   investigation. 
Acknowledgements. 

CHAPTER  I.     The    History    of    Investigation    and    Classification    of 

the  Pleistocene  of  Iowa. 
Early  students  of  the  drift. 

D.  D.  Owen. 

J.  H.  Hall. 

A.  W.  Worthen. 

C.  A.  White. 

T.  C.  Chamberlin. 

W  J  McGee. 

Chamberlin's  classification  of  the  Pleistocene. 
Work  of  Iowa  geologists. 

Discovery  of  the  Illinoian  drift  by  Leverett. 
Chamberlin's  revised  classification  of  the  Pleistocene. 
Introduction  of  the  terms  Yarmouth,  Sangamon  and  Peorian. 
Introduction  of  the   term  Nebraskan. 
The  lowan  drift  questioned. 
Calvin's  reply  to  critics  of  the  lowan. 
Work  of  Alden  and  Leighton. 

Geological  investigations  in  northeast  Iowa  by  A.  C.  Trowbridge. 
Carman's  work  in  northwest   Iowa. 
Work  of  Dr.   G.  F.   Kay. 

Table  showing  history  of  the  classification  of  the  early  Pleis- 
tocene of  Iowa. 

Classification  of  Pleistocene  deposits  as  used  recently  in  a 
report  of  the  Iowa  Geological  Survey  prepared  in  cooper- 
ation with  the  United  States  Geological  Survey. 

Bibliography. 


4657V-J 


CHAPTER    II.     The    Drift-Sheets    of    Iowa. 

Classification  of  Pleistocene  deposits  as  used  recently  in  a 
report  of  the  Iowa  Geological  Survey  prepared  in  cooper- 
ation with  the  United  States  Geological  Survey. 

A  study  of  the  various  drifts. 
Nebraskan   Drift. 
Kansan  Drift. 
Illinoian  Drift, 
lowan    Drift. 
Wisconsin   Drift. 

CHAPTER  III.     The  Interglacial   Deposits   of  Iowa. 

Classification  of  Pleistocene  deposits  as  used  recently  in  a 
report  of  the  Iowa  Geological  Survey  prepared  in  cooper- 
ation with  the  United  States  Geological  Survey. 

Basis  for  making  divisions  in   the  Pleistocene  Period. 

Criteria  used  in  establishing  interglacial  epochs. 

The   interglacial   epochs. 

Aftonian  interglacial  epoch. 
Yarmouth  interglacial  epoch. 
Sangamon  interglacial  epoch. 
Peorian  interglacial  epoch. 

CHAPTER  IV.     The  Loess. 

Early  discovery  of  the  loess  and  introduction  of  term. 
First  studied  in  the  United  States  by  Sir  Chas.  Lyell. 
Early  workers  on   the   loess   in  Iowa. 

D.  D.  Owen. 

W.  H.  Pratt. 

C.  A.  White. 

J.  E,  Todd. 

F.  M.  Witter. 

W  J  McGee. 
Work  of  T.  C.  Chamberlin  and  R.  D.  Salisbury  in  the  "Driftless 

Area." 

The  study  of  the  loess  by  Professor  Shimek. 
The  study  of  the  loess  by  other  Iowa  geologists. 
Theories  advanced  for  the  genesis  of  the  loess. 
The  age  of  the  loess  as  interpreted  by  geologists. 
Geographical  distribution  of  loess  within  the  state. 
Stratigraphic  relation  of  the  loess  to  the  various  drift-sheets. 
Oxidation    and   leaching   of   the    loess,   criteria   for    determining 

its  age. 

The  fossil  life  of  the  loess,  its  value. 
Summary. 

CHAPTER  V.     The   Peorian   Interglacial   Epoch. 
Work  of  Leverett  in  Illinois. 
The  value  of  the  Toronto  beds. 
A  comparison  of  the  life  of  the  Mahomet  beds  with  that  of  the 

Scarboro  beds. 
The  topographic  features  of  the  Wisconsin  drift  compared  with 

the  topographic  features  of  the  lowan  drift. 
Leaching  and  oxidation  of  the  Wisconsin   and  lowan  drifts. 
State  of  erosion  of  lowan  and  Wisconsin  drifts  contrasted. 
Weathering  of  the  Wisconsin  and  lowan  gravels. 
Stratigraphic  relation  of  the  Wisconsin  drift  to  the  lowan  drift. 
The    Peorian    interglacial    deposits    and    their   significance. 
Summary. 


ILLUSTRATIONS. 


1.  Buchanan  gravels,   Independence,   Buchanan   county. 

2.  Mature  erosion  of  Kansan  drift,  Washington  county. 

3.  Young  valleys  in  Illinoian  drift  plain. 

4.  Granite  bowlders  on  lowan  drift  plain. 

5.  Typical  undissected  lowan  drift  plain,  Howard  county. 

6.  Mantled  lowan  topography  contrasted  with  Kansan  topography. 

7.  Typical  Wisconsin  drift  plain,  Kossuth  county. 

8.  Deposits  of  Aftonian  gravels  near  Afton  Junction. 

9.  Soil  and  vegetable  zone  between  Kansan  and  Wisconsin  drifts. 

10.  Kansan  loess  topography  near  lowan  border. 

11.  Loess  bordering  the  Kansan  areas,  near  Osage,  Mitchell  county. 

12.  lowan  drift  capped  by  loess. 

13.  Relation  of  the  loess  to  the  Kansan  and  Wisconsin  drifts. 

14.  Section  in  brick  yard,  Iowa  City. 

15.  Fossils  of  the  loess. 

16.  Loess  showing  loess  kindchen  and  iron  concretions. 

17.  Drift  cut  west  of  Rhodes,  Marshall  county. 

18.  Loess  section,  Winneshiek  county. 

19.  Fossil  life  of  the  loess. 

20.  Peorian  cut  showing"  fossiliferous  loess  on  Sangamon  soil. 


INTRODUCTION. 

The  purpose  of  this  paper  is  to  present  some  of  the  chief  facts 
regarding  the  Pleistocene  of  Iowa,  in  connection  with  which  special 
reference  will  be  given  to  the  Peorian  Interglacial  Epoch.  It  will 
be  shown  that,  just  as  in  the  case  of  the  earlier  interglacial  epochs, 
there  are  definite  criteria  by  which  the  Peorian  Interglacial  Epoch 
can  be  recognized.  Moreover,  evidence  of  a  distinctive  character 
will  be  presented  with  regard  to  the  duration  of  the  Peorian  epoch. 

Before  field  investigations  were  begun,  the  literature  bearing 
on  the  subject  was  reviewed  carefully.  Much  helpful  information 
was  obtained  from  personal  interviews  with  Dr.  G.  F.  Kay,  who  has 
made  a  careful  study  of  the  Pleistocene,  particularly  in  southern 
Iowa;  Prof.  H.  F.  Wickham,  Department  of  Entomology,  State  Uni- 
versity of  Iowa,  who  has  studied  fossil  insects  from  interglacial 
deposits;  Dr.  M.  M.  Leighton,  who  has  worked  on  the  lowan  drift; 
W.  H.  Schoewe,  Assistant  in  the  Department  of  Geology,  State  Uni- 
versity of  Iowa,  and  others.  Parts  of  two  seasons  were  devoted  to 
field  investigation  during  which  time  the  regions  most  closely 
related  to  the  problem  were  examined  carefully.  Thorough  exam- 
inations were  made  of  cuts,  well  logs,  borings  and  surface  deposits. 
Sixty  auger  borings  were  made  along  the  border  of  the  Wisconsfn 
and  lowan  drifts,  to  determine  the  relative  amounts  of  leaching  of 
the  two  drift  sheets.  Trips  were  made  to  different  parts  of  the 
state  to  study  the  loess. 

Field  work  was  done  chiefly  along  the  margin  of  the  lowan  and 
Wisconsin  drifts  from  Worth  county  to  Hardin  county  a^d  where 
the  loess  which  is  related  to  the  lowan  drift  pas  es  beneath  the 
Wisconsin  drift. 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  7 

CHAPTER  I. 

THE   HISTORY  OF   INVESTIGATION   AND   CLASSIFICATION  OF 
THE  PLEISTOCENE  OF  IOWA. 

Dr.  (1)  D.  D.  Owen  was  the  first  person  to  give  careful  attention 
to  the  drift  of  Iowa.  Early  in  1848,  after  having  traveled  over  the 
northeastern  part  of  the  state,  he  became  interested  in  the  presence 
of  numerous  (granitic  bowlders  scattered  here  and  there  over  the 
surface.  It  became  his  firm  belief  that  these  enormous  granite 
masses  could  have  been  transported  to  the  position  in  wnich  they 
are  now  found  only  by  floating  ice,  which  must  surely  have  been 
drifted  in  from  the  north  before  the  land  of  this  area  emerged 
from  the  sea. 

During  the  years  that  James  Hall  served  as  state  geologist, 
much  of  his  time  was  devoted  to  the  study  of  the  indurated  rocks. 
He  was  more  interested  in  the  problems  associated  with  Stratig- 
raphy and  Paleontology  than  in  the  problems  of  the  Pleistocene. 
His  assistant,  A.  W.  Worthen,  had,  however,  observed  frequently 
the  surface  drift  with  its  numerous  erractics,  but  made  no  attempt 
to  explain  their  distribution. 

(2)  C.  A.  White,  in  1867,  was  the  first  state  geologist  to  give  any 
detailed  consideration  to  the  Pleistocene.     He  recognized  the  glacial 
origin    of    the    surface    deposits    and    referred    some    of    the    erratics 
found   in   them   to  their  true   sources  in   the  granitic  and  quartzitic 
ledges  lying  in  regions  to  the  north.     Further  than  this  he  made  no 
attempt  to  separate  the  various  drifts  into  their  respective  ages. 

(3)  T.  C.  Chamberlin  was  the  first  geologist  in  America  to  advance 
definitely   the   idea  of   the   duality   of   the   Pleistocene.     As   early   as 
1876,  he  recognized  a  first  and  second  glacial  epoch  with  a  distinct 
interglacial    epoch    between    them.      Later    he    published    his    views, 
but  at  the  time,  gave  no  names  to  the  deposits. 

(4)  W  J  McGee  introduced  methods  of  investigation  in  Iowa  which 
furnished  finally  the  key  to  the  interpretation  of  the—drift  deposits 
found    within    the    state.      After    having    traveled    extensively    over 
northeastern  Iowa,  he  became  convinced  that  there  were  two  drifts 
within    tne    region,    and    to    these    he    gave    the    names    "Lower"    and 
"Upper"    tiU,    both   of   which    are    earlier    than    Chamberlin's   second 
glacial    epoch.      He    believed    his    "Upper"    till    to   be,    in    general,    a 
continuous  ground  moraine,  composed,  for  the  most  part,  of  a  sheet 
of  bowldery  clay,  yellow,   buff,  or  brown  in  color.     The  entire  mass 
showed    itself    to   be    interspersed   with    subangular   or    rounded   and 
sometimes    striated    pebbles    and    bowlders,    the    greater    portion    of 
which    he   believed    to    have   come    from   beyond    the   borders   of   the 
state.     He   made   note   of  the    fact    that    the   structure   of   the   drift, 
like    that    of    ice-formed    deposits    elsewhere    observed    by    him,    was 
homogeneous   in   a  large  way,    though   heterogeneous   in   detail.      He 
observed  further,  that  the  thickness  of  the  drift  ranged  from  a  thin 
veneer  in   places   to  possibly  a  hundred  feet  or  more   in  others  and 
that   toward  its  periphery,  especially  southward,   the  "Upper"  drift- 
sheet  underwent  great  modification.     This  modification  was  revealed 
in    the    gradual    disappearance    of    the    surface    bowlders,    the    finer 
disintegration   of   the   drift    materials   and    a   characteristic   longitu- 
dinal ridging  of  the  surface  topography. 

It  was  found  that  the  superficial  portion  of  the  drift-sheet 
passed  insensibly  into  loam,  and  that  the  glacial  deposit  either 


8  EARLY  STUDENTS  OF  THE  DRIFT 

graded  up  into  a  superimposed  mantle  of  loess  or  was  overlain  by 
the  loess  unconformably,  though  frequently  an  intermediate  bed  of 
material  was  present.  It  was  his  firm  belief  that  the  "Lower"  till 
was  analogous  to  the  "Upper"  till  in  composition  and  distribution, 
though  the  continuity  of  the  "Lower"  till  was  more  broken.  The 
materials  are  much  the  same  though  he  noted  the  prevailing  color 
was  blue  and  the  alternative  color  brown.  It  was  observed  also  that 
the  pebbles  were  more  numerous  than  in  the  "Upper"  till-sheet, 
that  the  granite  bowlders  were  almost  absent  and  that  throughout 
the  mass  greenstones  predominated.  In  thickness  the  "Lower"  till 
was  found  to  vary  from  a  thin  veneer  up  to  more  than  200  feet, 
so  that  in  spite  of  its  frequent  breaks,  its  average  thickness  was 
about  twice  as  great  as  that  of  the  "Upper"  till.  It  was  found  that 
it  possessed  a  more  modified  periphery  than  the  "Upper"  till.  To- 
ward its  margin  it  differentiated  into  a  lower  member,  composed 
for  the  most  part  of  clay,  often  laminated,  and  showing  frequently 
evidences  of  water  deposition.  Since  the  "Lower"  till  was  not  a 
surface  exposure  in  northeastern  Iowa,  it  could  best  be  studied  only 
in  cuts  and  well  sections.  Wherever  examined  carefully,  it  was 
found  to  grade  upward  into  a  soil  or  bed  of  humus  charged  with 
remains  of  an  ancient  forest.  The  identifiable  remains  are  chiefly 
coniferous  woods,  though  fragments  of  other  hard  woods,  impres- 
sions of  leaves  and  traces  of  other  vegetation  are  frequently  found. 
These  vestiges  of  an  ancient  soil  and  its  products  are  so  widespread 
as  to  prove  beyond  doubt,  that  the  older  drift  was  covered  with  soil 
and  clothed  largely  with  forests  before  the  advance  of  the  "Upper" 
till  ice-sheet.  McGee  believed  that  his  "Lower"  drift  might  be 
Miocene-Tertiary  in  age,  and  that  the  interval  represented  by  the 
forest  bed,  which  he  reasoned  must  have  been  of  great  length, 
might  include  all  Pliocene  time.  As  a  result  of  McGee's  work  there 
was  made  for  the  first  time  in  northeast  Iowa  a  separation  of  the 
drift  into  a  "Lower"  and  "Upper"  till.  McGee  had  read  Chamber- 
lin's  report  of  Wisconsin  wherein  he  had  divided  the  Pleistocene 
into  two  distinct  glacial  epochs  with  an  intervening  epoch  of 
deglacation.  It  was  with  this  classification  of  Chamberlin  in  mind 
that  he  named  his  lower  dfift  "Lower"  till  and  his  upper  drift 
"Upper"  till.  McGee  thus  looked  upon  his  forest  bed  as  a  plane  of 
division  between  his  "Lower"  and  "Upper"  till-sheets  and  the 
equivalent  in  time  of  Chamberlin's  interglacial  epoch.  He  was  not 
aware  at  this  time  that  his  "Lower"  till  contained  not  one  but  two 
distinct  drift-sheets,  and  that  it  was  between  these  two  that  the 
forest  bed  he  described  so  well  was  located. 

In  1894,  after  further  study  of  the  Pleistocene,  (5)  T.  C.  Chamber- 
lin in  his  discussion  of  the  "Glacial  Phenomena  in  North  America," 
advanced  a  threefold  classification  for  the  Pleistocene  of  Iowa, 
wherein  he  called  the  outermost  drift  Kansan,  and  in  writing  of  it 
says  "this  drift-sheet  reaches  its  maximum  southerly  extension  in 
Illinois,  and  it  would  seem  most  appropriate  to  select  a  name  for 
this  formation  from  this  apex.  There  are,  however,  in  some  places, 
two  distinct  drift-sheets  separated  by  a  soil  horizon,  and  since  it  is 
not  yet  satisfactorily  determined  whether  this  division  is  widespread 
and  important,  or  merely  local,  it  is  not  thought  advisable  to 
entertain  a  name  for  the  formation  from  this  locality.  Perhaps  the 
extension  of  the  ice  southwesterly  in  the  direction  of  the  great  arid 
plains,  is  equally  worthy  of  consideration.  While  the  formation  in 
Kansas  is  subordinately  divisible,  it  appears  to  be  an  essential 
unity,  and  for  this  reason  the  name  Kansan  has  been  selected  for 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA.  9 

present  use  as  a  convenient  designation  for  the  outermost  drift- 
sheet."  Overlapping-  the  Kansan,  but  separated  from  it  by  a  well 
defined  soil  line  lies  a  second  and  similar  drift-sheet  which  he 
termed  East-Iowan  since  it  had  been  most  carefully  worked  out  by 
McGee  in  northeastern  Iowa  and  there  displayed  its  most  distinct- 
ive topographical  and  lithological  characteristics.  Overlapping  the 
East-Iowan,  and  separated  from  it  by  a  well  marked  soil  line  and 
vegetable  accumulation,  oxidized  and  ferruginated  zones  and  ero- 
sional  surface  is  a  third  drift  which  he  termed  East-Wisconsin. 
The  name  East-Wisconsin  was  chosen  since  this  drift-sheet  assumed 
some  of  its  most  prominent  surface  topography  and  development  in 
eastern  Wisconsin.  Later  at  the  suggestion  of  Upham,  the  terms 
East-Iowan  and  East-Wisconsin  were  changed  to  "lowan"  and 
"Wisconsin."  McGee  and  Chamberlin  spent  some  time  inves- 
tigating the  drift  in  Iowa,  giving  especial  attention  to  the  deposits 
in  the  vicinity  of  Afton  Junction.  After  having  studied  carefully 
the  type  sections  here,  the  following  interpretation  was  reached: — 
The  upper  surface  drift  exposed  directly  beneath  the  loess  was 
taken  to  be  the  equivalent  of  McGee's  "Upper"  till  of  northeast 
Iowa,  while  the  lower  drift  beneath  the  gravel  deposits  was 
interpreted  to  be  McGee's  "Lower"  till  of  northeast  Iowa.  It 
was  their  belief,  at  this  time,  that  the  upper  drift  at  Afton 
Junction,  East-Iowan  of  Chamberlin,  did  not  extend  southward 
much  beyond  Afton  Junction,  while  the  lower  till-sheet  here  ex- 
tended much  further  to  the  south,  and  hence  into  Kansas  where  it 
became  the  surface  drift  and  exhibited  its  most  striking  surface 
characteristics,  hence  the  name  Kansan.  The  interglacial  deposits 
of  sand  and  gravel  found  at  Afton  Junction  were  taken  to  be  the 
equivalent  of  McGee's  "forest  bed"  in  northeastern  Iowa,  thus  the 
name  Aftonian.  It  (6)  should  be  noted  here  that  in  the  original  paper 
by  Chamberlin,  the  term  Aftonian  was  not  applied  to  the  gravels 
which  form  so  conspicuous  a  feature  of  the  Afton-Thayer  cuts. 
These  gravel  deposits  were  considered  to  represent  rather  kame-like 
accumulations  upon  the  surface  of  the  lower  and  older  drift-sheet. 

As  a  result  of  the  work  of  Chamberlin  and  McGee-the  following 
classification  of  the  Pleistocene  may  be  presented  to  represent  their 
views: — 

Chamberlin's  Earliest  Classification   of   the   Glacial   Period. 
Second   Glacial   Epoch. 

First  Interglacial  Epoch. 
First    Glacial    Epoch. 

McGee's  Classification  McGee  and  Chamberlin 

of  Northeast   Iowa.  at  Afton   Junction. 

"Upper"  till   (Chamberlin's  East-Iowan) lowan. 

Forest    bed Aftonian. 

"Lower"    till Kansan. 

After  the  work  of  Chamberlin  and  McGee  at  Afton  Junction,  a 
number  of  the  Iowa  geologists,  more  particularly  Bain  and  Calvin, 
after  much  detailed  work  had  been  done  on  the  drifts  of  the  state, 
reached  the  conclusion  that  the  upper  of  the  two  drift-sheets,  at 
the  Afton  Junction  section,  was  equivalent  to  McGee's  "Lower"  till 
of  northeastern  Iowa,  that  the  "Upper"  till  of  McGee's  area,  East- 
Iowan  of  Chamberlin,  was  not  present  at  Afton  Junction,  and  that 
the  lower  drift  at  Afton  Junction  was  distinct  from  any  of  the 
drift-sheets  recognized  in  northeastern  Iowa.  The  Afton  Junction 


10 


WORK  OF  IOWA  GEOLOGISTS 


region  was  la^er  visited  by  T.  C.  Chamberlin  in  company  with  other 
Iowa  geologists,  and  Bain's  conclusions  were  confirmed.  After  the 
work  of  the  Iowa  geologists  at  Afton  Junction,  they  applied  the 
term  lowan  to  the  "Upper"  till  of  McGee's  area,  which  they  agreed 
did  not  extend  to  the  Afton  Junction  region.  Professor  Calvin  then 
interpreted  McGee's  area  as  follows: — The  "Lower"  till  of  McGee's 
area  is  separated  from  the  "Upper"  till  by  a  distinct  forest  bed,  but 
the  Iowa  geologists  had  shown  that  McGee's  forest  bed,  instead  of 
lying  between  the  "Upper"  and  "Lower"  till-sheets,  lies  between 
two  drift-sheets,  both  of  which  are  to  be  found  below  McGee's 
"Upper"  till.  There  are  therefore,  in  the  northeastern  area  of 
McGee,  three  CO  drift-sheets  instead  of  two  as  reported  by  McGee,  and 
his  forest  bed  lies  between  the  two  lower  till-sheets  instead  of 
between  the  "Upper"  till  and  the  "Lower"  till. 

(6)  Calvin,  in  his  study  in  McG  :e's  area,  had  noted  extensive  gravel 
deposits  lying  between  McGee's  "Upper"  till  and  "Lower"  till-sheets. 
These  gravels  were  first  recognized  as  a  distinct  interglacial  form- 
ation at  the  Illinois  Central  gravel  pit,  located  in  the  northwest 
quarter  of  section  32,  Byron  Township,  Buchanan  county,  Iowa. 


Plate  I. 

Buchanan   Gravels    (Calvin). 

When  these  gravels  were  first  studied,  in  1896,  it  was  the 
current  belief  that  there  had  been  but  two  ice  invasions,  except  in 
the  region  occupied  by  the  Wisconsin  lobe.  As  the  Aftonian 
gravels  were  thought  to  hold  an  intermediate  position  between  the 
"Upper"  and  "Lower"  till-sheets,  and  since  the  Buchanan  gravels 
occupied  plainly  what  seemed  to  be  a  similar  position,  they  were 
first  referred  to  the  Aftonian  stage.  After  the  work  of  the  Iowa 
geologists  who  had  proven  that  the  till  overlying  the  Aftonian  beds 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  n 

at  Afton  Junction  was  Kansan,  the  "Lower"  till  of  McGee's  area  and 
not  the  lowan  or  "Upper"  till,  as  had  been  assumed,  a  readjustment 
became  necessary.  A  new  adjustment  in  terms  was  made  and  the 
Aftonian  deposits  were  assigned  to  their  true  position  beneath  the 
Kansan.  The  Buchanan  .gravels  were  then  placed  as  representative 
deposits  of  the  second  interglacial  epoch.  (5)  T.  C.  Chamberlin,  in 
1895,  had  published  his  classification  of  American  glacial  deposits 
wherein  he  recognized  the  Kansan,  lowan,  and  Wisconsin  ice-sheets. 
It  was  in  these  publications  that  the  Aftonian  beds  were  referred 
to  the  interval  between  the  Kansan  and  the  lowan.  After  Bain's 
work,  and  the  adjustment  that  followed,  the  Buchanan  gravels  were 
left  as  the  only  recognized  deposit  of  this  interval  in  northeast 
Iowa.  It  should  be  noted  here  that  the  use  of  the  term  Buchanan 
for  a  second  interglacial  epoch  is  open  to  question,  since  at  the 
time  of  its  introduction,  the  Illinoian  ice-sheet  had  not  been  estab- 
lished. 

After  a  detailed  study  of  the  drift  in  southeastern  Iowa  and 
southern  Illinois,  (9)  Leverett  discovered  a  till-sheet  older  than  the 
lowan  but  younger  than  the  Kansan.  The  term  Illinoian  was  first 
used  by  him  in  1894,  in  his  correspondence  with  his  colleagues,  it 
being  his  desire  not  to  introduce  the  term  into  literature  until 
some  of  the  leading  geologists  had  seen  the  drift  and  verified  his 
conclusions.  In  August,  1896,  T.  C.  Chamberlin  and  H.  F.  Bain,  in, 
company  with  Mr.  Leverett,  visited  some  of  the  exposures  where 
the  drift  was  best  shown  and  each  arrived  at  the  conclusion  that  it 
was  necessary  to  introduce  a  distinctive  name  for  the  newly  discov- 
ered drift-sheet.  The  term  Illinoian  was  first  introduced  into  liter- 
ature by  T.  C.  Chamberlin,  in  1896,  though  he  gives  Mr.  Leverett 
credit  for  suggesting  the  term. 

Because  of  the  more  recent  discoveries  in  the  Pleistocene,  (10)  T.  C. 
Chamberlin,  in  1896,  revised  his  classification,  recognizing  five  drift- 
sheets  instead  of  three.  Shortly  after  the  discovery  of  the  Illinoian 
drift,  Mr.  (H)  Leverett  reported  the  finding  of  a  soil  zone  containing 
small  bones  underlying  immediately  this  drift-sheet,  to  which  he 
applied  the  term  Yarmouth,  since  the  well  section  in  winch  the  soil 
zone  was  discovered,  was  located  near  the  village  of  Yarmouth, 
Des  Moines  county,  Iowa,  and  because  the  name  of  the  village  is 
less  likely  to  be  confusing  than  names  which  are  common. 

The  term  Sangamon,  representing  the  third  interglacial  epoch, 
was  first  introduced  into  literature  by  Mr.  (12)  Leverett,  in  1896.  Since 
the  earliest  recognition  of  the  occurrence  of  a  definite  soil  horizon, 
between  what  is  assumed  to  be  lowan  loess  and  Illinoian  till,  was 
first  discovered  in  Sangamon  county,  Illinois,  it  was  agreed  by  T.  C. 
Chamberlin  and  Mr.  Leverett,  that  the  most  fitting  term  by  which 
to  designate  the  deposit  should  be  Sangamon.  With  this  discovery 
Mr.  Leverett  suggested  that  since  there  was  no  Illinoian  glacial 
stage  to  break  the  continuity  of  interglacial  conditions  in  McGee's 
area,  that  the  term  Buchanan  gravels  covered  but  a  small  time 
between  the  retreat  of  the  Kansan  ice  and  the  lowan  advance. 
But  since  there  was  an  interglacial  interruption  between  the 
Kansan  and  the  lowan  ice-invasions,  there  is  need  for  names  which 
will  stand  for  the  weathered  zones  above  and  below  the  Illinoian 
till-sheet,  hence  the  name  Sangamon. 

The  term  Peorian  was  first  introduced  into  literature  by  T.  C. 
Chamberlin  to  designate  those  deposits  of  interglacial  age  lying 
between  lowan  loess  and  deposits  of  early  Wisconsin  age,  though 
the  discovery  of  the  deposits  was  made  by  Mr.  (13)  Leverett.  The  type 


14  BIBLIOGRAPHY 

3.     Kansan  drift   (of  Iowa  geologists) 

2.  Aftonian  gravels,  vegetal  deposits,  soil  and  weathered 
zone  (of  Chamberlin)  (including  super-Nebraskan 
"gumbo,"  or  "gumbotil"  of  Kay)  at  top  of  Nebras- 
kan  drift 

i.     Nebraskan    drift    (of    Iowa    geologists)     (pre-Kansan    or    sub- 
Aftonian  of  Chamberlin) 


BIBLIOGRAPHY. 

1.  D.  D.  Owen.     Report  of  a  Geological  Survey  of  Wisconsin  and 

Minnesota,   p.    144,    1852. 
S.  Calvin.     Proc.  la.  Acad.  Sciences,  Vol.  5,   1898,  p.  64. 

2.  C.    A.    White.     Report    of    the    Geological    Survey    of    Iowa,    by 

J.  H.  Hall  and  J.  D1.  Whitney,   1858.,  pp.  187,  200,  210,  221. 

3.  T.  C.  Chamberlin.     Geology  of  Wisconsin,  Vol.  I. 

4.  W  J   McGee.     Eleventh   Annual    Report   U.   S.    Geological   Sur- 

vey,   1893,   p.    192. 

5.  T.    C.    Chamberlin.      Amer.    Jour.    Science,    Vol.    45    third    aeries, 

p.  197. 

6.  H.  F.  Bain.     Proc.  la.  Acad.  Sciences,  Vol.  5,  1898,  p.  87. 

7.  S.  Beyer.     Proc.  la.  Acad.  Sciences,  Vol.  4,   1897,  p.  58. 

8.  S.  Calvin.     Proc.  la.  Acad.  Sciences,  Vol.  5,  1898,  p.  66. 

S.  Calvin.     Buchanan      gravels     and      interglacial      deposit      in 
Buchanan  county,  Amer.  Geologist,  Vol.  17,  1898,  pp.  76-78. 

9.  F.  Leverett.     Introduction  of  the  term  Illinoian. 

Proc.  la.  Acad.  Sciences,  Vol.  5,   1898,  p.  73. 

10.  T.  C.  Chamberlin.     Classification  of  the  Pleistocene. 

Jour,  of  Geology,  Vol.  4,   1896,  p.  874. 

11.  F.  Leverett.     The    weathered     zone     (Yarmouth)     between     the 

Illinoian   and   Kansan    till-sheets.      Proc.    la.   Acad.   Sciences, 
^     Vol.  5,   1898,  p.  81. 

Jour,  of  Geology,  Vol.  6,   1898,  p.   238. 

12.  F.  Leverett.     The    weathered    zone     (Sangamon)     between     the 

lowan    loess    and    the    Illinoian    till-sheet.      Proc.  .  \a.    Acad. 
Sciences,  Vol.  5,   1898,  p.  71. 

13.  F.  Leverett.     The  Peorian  interglacial   epoch.   , 

Monograph  U.  S.  Geol.  Survey,  Vol.  38,   1898,  pp.  185-190. 
Jour,   of   Geology,   Vol.    6,    1899,   pp.    244-249. 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA      .       15 

14.  F.  Leverett.     "Weathering-    and    Erosion    as    Time    Measurers," 

Amer.  Jour.  Science,   third  series,  Vol.   27,   1909. 
"Comparison    of    North     American     and     European    Glacial 
Deposits,"    1910. 

15.  S.   Calvin.     The   lowan   drift.     Jour,   of  Geology,   Vol.    19,    1911, 

PP-   577-602. 

16.  Alden  &  Leighton.     The  lowan  drift,  a  review  of  the  evidence 

of   the  lowan   stage  of  glaciation.     la.   Geol.  Surv.   Reports, 
Vol.   26,    1915,   pp.   55-213. 

17.  A.    C.    Trowbridge.      Preliminary    report   on    geological   work   in 

northeastern   Iowa.      Proc.   la.   Acad.   Sciences,   Vol.   21,    1914, 
pp.   205-211. 

18.  J.   E.  Carman.     The   Pleistocene  geology  of  northwestern   Iowa. 

la.  Geol.  Surv.  Reports,  Vol.  26,   1915,  pp.  239-445. 

19.  G.  F.  Kay.     Gumbotil  a  new  term  in  Pleistocene  geology. 

Science  new  series,  Vol.   44,    1916,  p.  637. 

20.  G.    F.    Kay.      Some    features    of    the    Kansan    drift    in    southern 

Iowa.     Bull.  Geol.  Soc.  America,  Vol.  27,   1916,  pp.   115-117. 

21.  Classification    of   the   Pleistocene   used    recently   in   a  report   of 

the   Iowa   Geological   Survey   prepared    in   cooperation    with 

the  United   States   Geological   Survey. 

la.  Geol.  Surv.  Reports,  Vol.  26,   1915,  pp.  56-57. 


14  BIBLIOGRAPHY 

3.     Kansan  drift   (of  Iowa  geologists) 

2.  Aftonian  gravels,  vegetal  deposits,  soil  and  weathered 
zone  (of  Chamberlin)  (including  super-Nebraskan 
"gumbo,"  or  "gumbotil"  of  Kay)  at  top  of  Nebras- 
kan  drift 

i.     Nebraskan    drift    (of    Iowa    geologists)     (pre-Kansan    or    sub- 
Aftonian  of  Chamberlin) 


BIBLIOGRAPHY. 

1.  D.  D.  Owen.     Report  of  a  Geological  Survey  of  Wisconsin  and 

Minnesota,   p.    144,    1852. 
S.  Calvin.     Proc.  la.  Acad.  Sciences,  Vol.  5,  1898,  p.  64. 

2.  C.    A.    White.     Report    of    the    Geological    Survey    of    Iowa,    by 

J.  H.  Hall  and  J.  D.  Whitney,   1858,  pp.  187,  200,  210,  221. 

3.  T.  C.  Chamberlin.     Geology  of  Wisconsin,  Vol.  I. 

4.  W   J   McGee.      Eleventh    Annual    Report    U.    S.    Geological    Sur- 

vey,   1893,   P-    T92- 

5.  T.    C.    Chamberlin.      Amer.    Jour.    Science,   Vol.    45    third  .series, 

p.  197. 

6.  H.  F.  Bain.     Proc.  la.  Acad.  Sciences,  Vol.  5,  1898,  p.  87. 

7.  S.  Beyer.     Proc.  la.  Acad.  Sciences,  Vol.  4,   1897,  p.  58. 

8.  S.  Calvin.     Proc.   la.  Acad.  Sciences,  Vol.  5,   1898,  p.  66. 

S.  Calvin.     Buchanan      gravels     and      interglacial      deposit      in 
Buchanan  county,  Amer.  Geologist,  Vol.  17,  1898,  pp.  76-78. 

9.  F.  Leverett.     Introduction  of  the  term  Illinoian. 

Proc.  la.  Acad.  Sciences,  Vol.  5,  1898,  p.  73. 

10.  T.  C.  Chamberlin.     Classification  of  the  Pleistocene. 

Jour,  of  Geology,  Vol.  4,   1896,  p.  874. 

11.  F.  Leverett.     The    weathered     zone     (Yarmouth)     between     the 

Illinoian   and   Kansan    till-sheets.      Proc.    la.   Acad.   Sciences, 
M     Vol.  5,   1898,  p.  81. 

Jour,  of  Geology,  Vol.  6,   1898,  p.   238. 

12.  F.  Leverett.     The    weathered    zone     (Sangamon)     between     the 

lowan    loess    and    the    Illinoian    till-sheet.      Proc.  .  la.    Acad. 
Sciences,  Vol.  5,   1898,  p.  71. 

13.  F.  Leverett.     The  Peorian   interglacial   epoch.  .', 

Monograph  U.  S.  Geol.  Survey,  Vol.  38,  1898,  pp.  185-190. 
Jour,   of   Geology,   Vol.    6,    1899,    pp.    244-249. 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA      .       15 

14.  F.  Leverett.     "Weathering-    and    Erosion    as    Time    Measurers," 

Amer.  Jour.  Science,   third  series,  Vol.   27,   1909. 
"Comparison    of    North     American     and     European    Glacial 
Deposits,"    1910. 

15.  S.   Calvin.     The   lowan   drift.     Jour,   of  Geology,   Vol.    19,    1911, 

PP-   577-602. 

16.  Alden  &  Leighton.     The  lowan  drift,  a  review  of  the  evidence 

of   the   lowan  stage  of  glaciation.     la.   Geol.  Surv.   Reports, 
Vol.   26,    1915,   pp.   55-213. 

17.  A.    C.   Trowbridge.      Preliminary    report   on    geological   work   in 

northeastern  Iowa.     Proc.   la.   Acad.   Sciences,  Vol.  21,    1914, 
pp.   205-211. 

18.  J.   E.  Carman.     The   Pleistocene  geology  of  northwestern   Iowa. 

la.  Geol.  Surv.  Reports,  Vol.  26,   1915,  pp.  239-445. 

19.  G.  F.  Kay.     Gumbotil  a  new  term  in  Pleistocene  geology. 

Science  new  series,  Vol.  44,    1916,  p.  637. 

20.  G.    F.    Kay.      Some    features    of    the    Kansan    drift    in    southern 

Iowa.     Bull.  Geol.  Soc.  America,  Vol.  27,   1916,  pp.   115-117. 

21.  Classification    of   the   Pleistocene   used    recently   in   a   report   of 

the   Iowa   Geological   Survey   prepared    in   cooperation    with 

the  United   States   Geological   Survey. 

la.  Geol.  Surv.  Reports,  Vol.  26,   1915,  pp.  56-57. 


16  A  STUDY  OF  THE  VARIOUS  DRIFTS 

CHAPTER    II. 

THE  DRIFT  SHEETS  OF  IOWA. 
CLASSIFICATION. 

It  is  quite  generally  agreed  that  Iowa  was  invaded  by  five  dis- 
tinct ice-sheets.  In  no  other  area  are  all  the  drifts  known  to  be 
represented  and  in  such  a  way  that  it  is  possible  to  study  one  drift 
in  relation  to  other  drifts. 

(^As  shown  in  Chapter  I  the  following  is -the  classification  of  the 
Pleistocene  deposits  that  was  used  recently  in  a  report  of  the  Iowa 
Geological  Survey  prepared  in  cooperation  with  the  United  States 
Geological  Survey. 

9.     Wisconsin  drift  (of  the  Des  Moines  lobe) 

8.     (b)    Peorian  soil  and  weathered  zone   (of  Leverett)    at 

top    of   loess    and   beneath    Wisconsin    drift 
(a)   Main  deposit  of  loess 
7.     lowan  drift   (of  Iowa  geologists) 

6.     Sangamon   soil,   vegetal   deposits,    and   weathered   zone 
(of    Leverett)     (including    super-Illinoian    "gumbo,"    or 
"gumbotil"    of   Kay)    at    top    of   Illinoian    drift    and 
beneath  loess 

5.     Illinoian  drift   (of  Leverett) 

4.  Yarmouth  soil,  vegetal  deposits,  and  weathered  zone 
(of  Leverett)  (including  super-Kansan  "gumbo,"  or 
"gumbotil"  of  Kay)  at  top  of  Kansan  drift;  also 
Buchanan  gravel  (of  Iowa  geologists)  beneath 
Iowa  drift  and  loess 

3.     Kansan  drift    (of  Iowa  geologists) 

2.  Aftonian  gravels,  vegetal  deposits,  soil  and  weathered 
zone  (of  Chamberlin)  (including  super-Nebraskan 
"gumbo,"  or  "gumbotil"  of  Kay)  at  top  of  Nebras- 
kan  drift 

i.     Nebraskan    drift    (of    Iowa   geologists)    (pre-Kansan    or    sub- 
Aftonian  of  Chamberlin) 

The  oldest  drift,  as  shown  by  the  above  classification,  is  the 
Nebraskan.  Being  the  (l)  oldest,  the  Nebraskan  is  for  the  most  part 
covered  by  younger  drifts.  That  the  drift  is  distributed  widely  over 
the  state  is  shown  by  data  obtained  from  deep  cuts  and  well  logs. 
Stratigraphically,  the  drift  lies  unconformably  beneath  the  Kansan 
and  upon  an  erosional  bed  rock  surface/  Recent  work  within  the 
"Driftless  Area"  of  Iowa,  by  (2)  A.  C.  Trowbridge,  of  the  State  Univer- 


SOME  PHASES  OF  THE,  PLEISTOCENE  OF  IOWA  17 

sity  of  Iowa,  has  revealed  two  distinct  peneplains,  the  upper  of 
which  has  been  called  the  Dodgeville  peneplain,  and  the  lower  the 
Lancaster  peneplain.  The  region  seems  to  have  been  invaded  by 
the  older  ice-sheets,  possibly  the  Nebraskan  and  the  Kansan.  O'n 
the  lower  plain  Professor  Trowbridge  has  found  a  highly  weathered 
and  oxidized  drift  which  he  seems  to  think  may  prove  to  be 
Nebraskan  drift.  Because  of  its  high  state  of  weathering  and 
oxidation,  it  becomes  very  difficult  to  distinguish  the  drift  from 
the  residual  material.  The  best  exposures  are  to  be  seen  along  the 
valley  walls.  The  relation  of  the  drift  to  the  two  peneplains  is 
shown  in  figure  (i). 


Figure  1. 


A  is   the  Dodgeville  plain,   B  the  Lancaster,   and  C  sections  of  the 

drift. 

That  the  drift  had  not  been  discovered  sooner  may  have  been 
due  to  its  high  state  of  weathering.  From  its  relation  to  the  Lan- 
caster plain,  it  seems  quite  conclusive  that  the  drift  must  have 
been  deposited  before  the  cutting  of  the  valleys  of  the  lower 
plain.  Lithologically  and  petrologically  there  is  a  wide  variation 
in  this  drift  from  place  to  place,  as  is  true  of  the  other  drifts.  In 
many  sections,  where  the  Nebraskan  has  been  studied,  (3)  it  is  a  dark 
bluish-black,  tough,  jointed  clay  containing  a  few  pebbles  and 
bowlders.  When  thoroughly  dry  it  breaks  with  a  starch-like  frac- 
ture into  small  angular  fragments,  and  becomes  exceedingly  hard.  J 

More  recent  investigations  by  (4).  J.  E.  Carman,  in  Cherokee  county 
reveal  this  same  drift  with  a  color  that  is  gray,  rather'  than  black, 
and  containing  tints  of  various  colors  such  as  chocolate,  brown, 
purple,  and  blue.  That  the  surface  of  this  old  drift  has  undergone 
marked  physical  change,  as  well  as  chemical  change,  is  shown  by 
the  fact  that  it  is  covered  by  gumbotil,  except  where  the  gumbotil 
is  eroded  away.  As  shown  by  Dr.  (5)  G.  F.  Kay,  the  thickness  of  the 


3 


i8 


A  STUDY  OF  THE  VARIOUS  DRIFTS 


gumbotil    varies    somewhat,    but    a    maximum     thickness    of    about 
thirteen  feet   is  known. 

The  drift  deposited  by  the  second  ice-invasion  is  known  as  the 
Kansan.  It  was  one  of  the  most  widespread  invasions  experienced 
by  the  North  American  Continent,  and  it  left  its  record  in  a  very 
widely  distributed  till-sheet.  While  possibly  no  more  widespread 
than  the  Nebraskan  in  Iowa,  it  has  a  much  wider  areal  distribution, 
since  over  considerable  areas  it  has  not  been  covered  by  later 
drifts.  Lithologically,  (6)  it  is  composed  of  a  compact,  tenacious  clay, 
which  when  dry,  shows,  like  the  Nebraskan,  a  highly  jointed  struc- 
ture. On  weathering  it  breaks  down  into  angular  "blocks  or  frag- 
ments. Distributed  through  the  body  of  the  till  are  numerous 
greenstones  and  granite  bowlders  varying  in  size  from  a  few  milli- 
meters up  to  a  foot  or  more.  A  drift,  exposed  at  the  surface  for 
long  periods  of  time,  should  show  a  high  state  of  oxidation  and 
leaching.}  That  this  is  true  of  the  Kansan  is  shown  in  figure  (2). 
The  lower  dotted  line  shows  the  average  depth  of  leaching  while 
the  upper  continuous  line,  shows  the  depth  of  oxidation. 


1 


i 


XfF, 


10  •• 


Figure    2. 


Curves  showing  depth  of  leaching  and  oxidation  of  the  drift-sheets. 

It  should  be  noted  that  averages  only  are  here  considered.     The 
great  depth  of  oxidation  and  leaching  shown  by   the  Kansan,   is  in 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  i-; 

harmony  with  its  great  age.  The  prevailing  color,  as  stated  previ- 
ously, is  blue  where  unoxidized.  Where  it  is  oxidized  thoroughly 
the  color  becomes  a  dark  yellowish  brown  or  brownish  red. 

Early  students  of  the  drift  thought  it  possible  to  distinguish 
one  drift  from  another  by  their  color  and  lithological  characters. 
Recent  investigation  has  proven  that  this  is  not  true  always.  It  is 
probably  true,  that  all  the  drifts  originally,  in  their  fresh  state, 
were  more  or  less  bluish  in  color,  and  that  the  yellowish  to  yellow- 
ish brown  to  brownish  red  colors  now  so  prevalent  on  the  surface 
of  the  various  drift-sheets  have  resulted  from  long  periods  of  con- 
tinued oxidation  and  leaching.  The  great  age  of  the  Kansan  drift 
is  shown,  by  its  high  state  of  oxidation  and  leaching,  and  by  its 
advanced  stage  of  mature  erosional  topogn  phy.  | 


Plate  II. 

Mature  erosion  of  Kansan  drift  plain,  Washington  county,  la.  (Alden) 

The  main  Kansan  area  is  a  region  in  which  there  are  well 
developed  valley  systems,  each  valley  system  having  primary,  sec- 
ondary, and  tertiary  tributaries.  Many  of  the  major  streams  have 
incised  their  channels  into  the  drift  to  a  depth  of  100  to  150  feet 
below  the  accordant  upland  level,  and  having  reached  grade,  they 
are  flowing  in^  wide,  sinuous  courses  across  the  old  Kansan  drift- 
plain.  Except  for  local,  wide  tabular  divides  found  in  the  southern 
part  of  the  state,  the  surface  is  reduced  wholly  to  slope  and  valley 
bottom  in  about  equal  proportions,  the  dissection  being  more 
marked  in  the  vicinity  of  the  major  streams.  The  undissected 
tabular  divides  found  between  the  streams,  as  for  example,  in 
Washing-ton  county,  are,  as  shown  by  Dr.  G.  F.  Kay,  but  remnants 
of  the  Kansan  gumbotil-plain.  These  tabular  divides  owe  their 
existence  to  the  fact  that  streams  have,  as  yet,  not  reached  them. 
The  divides  are .  conspicuous  topographic  features,  being-  very  flat 
and  poorly  drained. 

The  ice-invasion  subsequent  to  the  Kansan,  is  known  as  the 
Illinoian.  This  ice-sheet  advancing  from  the  Labradorean  center, 


20  A  STUDY  OF  THE  VARIOUS  DRIFTS 

crossed  the  state  of  Illinois  and  pushed  beyond  the  Mississippi  river, 
into  the  southeastern  part  of  Iowa.  The  lithological  characters  of 
the  Illinoian  drift  are  much  the  same  as  those  of  the  Kansan  drift. 
It  is  composed  largely  of  cl.ay,  with  some  sand  and  gravel.  The 
prevailing  color  of  the  weathered  drift  is  yellowish  brown  near  the 
surface  but  beneath  it  passes  into  the  blue  gray  till.  It  will  be 
seen  from  figure  (2),  that  the  drift  shows  an  average  leaching  and 
oxidation  of  8  and  15  feet  respectively.  As  to.  the  amount  of  erosion 
shown  by  the  Illinoian  drift  wrhen  contrasted  with  the  Kansan  and 
lowan  drift  areas,  it  may  be  said  that  in  Iowa  the  Illinoian  drift 
plain  presents  bro^d  upland  areas  quite  flat  and  of  greater  extent 
than  similar  divides  in  the  adjoining  Kansan  area.  That  portion 
of  the  Illinoian  plain  located  in  southeastern  Iowa  and  across  the 
Mississippi  river  in  Illinois,  being  near  to  the  major  drainage  line 
in  the  Mississippi  basin,  is  dissected  by  pronounced  valleys  of 
great  depth.  Away  from  the  major  drainage  line,  where  the 
streams  have  gentle  gradients,  the  surface  of  the  Illinoian  drift  is 
relatively  flat  with  slight  undulations.  Few  drainage  lines  are  pres- 
ent, and  when  present,  they  have  always  a  youthful  appearance. 
Near  the  Mississippi  river,  however,  in  both  Illinois  and  Iowa,  the 
surface  of  the  Illinoian  drift  is  characterized  by  -broad,  flat  upland 
divides  and  deep  vaPeys  with  numerous  deep  incised  tributary 
valleys.  The  valleys  of  the  major  streams  have  a  depth  of  100  to 
150  feet,  with  well  pronounced  flood-plains.  Contrasted  with  the 


Plate  III. 

Young  valleys  on  Illinoian   drift,   Fairview  Sheet,   Illinois.      (Alden) 

lowan    drift    topography,    the    Illinoian    drift-sheet    would    seem    to 
show  considerably   more   erosion.     The   lowan  drift   is  not  dissected 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  21 

by  such  sharp  cut  valleys,  the  slopes  are  more  gentle,  and  the 
entire  area  gives  the  impression  of  a  drift  younger  than  the 
Illinoian. 

Subsequent  to  the  Illinoian,  came  the  fourth  ice-invasion, 
known  as  the  lowan.  It  had  its  origin  in  the  Keewatin  center, 
entered  the  northeastern  part  of  the  state,  and  extended  approx- 
imately as  far  south  as  the  Iowa  river.  The  total  area  covered  by 
this  sheet  was  about  9000  square  miles,  or  one  seventh  the  entire 
area  of  the  state.  On  the  west,  this  drift  sheet  is  bounded  by  the 
Wisconsin,  while  on  the  east  it  in  no  place  reaches  the  Illinoian 
drift,  except  in  Clinton  county,  where  a  tongue  of  the  lowan 
reached  possibly  to  the  Mississippi  river.  Since  recent  investigation 
into  the  lithological  composition  of  the  drift-sheets  has  shown  them 
to  be  very  similar,  it  will  be  rather  difficult  to  determine  accurate- 
ly the  eastern  and  southern  margins  of  the  lowan  drift.  Its  margin, 
no  douBt,  is  lobate,  rather  distinct  in  places,  while  in  others  it  is 
difficult  to  outline.  All  'evidence  points  to  a  thin  ice-sheet,  which 
was  devoid  of  any  marked  terminal  moraine.  The  drift  is  largely 
clay,  with  locally  a  mixture  of  sand  and  gravel.  The  common 
pebbles  are  greenstones,  limestones,  schists,  quartzites,  cherts  and 
sandstones.  One  of  the  outstanding  differences  between  this  drift 
and  all  others,  is  the  presence  of  many  immense  granite  bowlders 
on  the  surface. 


Plate  IV. 

lowan   bowlder  west   of  Cedar   Falls. 

They  are  prevailingly  coarse  grained,   both  dark  and  light  col- 
ored, though  the  light  colors  predominate,  and  show  little  effect  of 


22  A  STUDY  OF  THE  VARIOUS  DRIFTS 

weathering.  Topographically,  the  bowlders  are  found  to  lie  on  the 
surface  without  respect  to  specific  location.  They  may  be  found  on 
the  .crests  of  gentle  swells,  on  the  slopes  of  flat  swales,  and  in  the 
bottom  of  shallow  depressions.  The  color  of  the  drift  is  dominantly 
a  light  yellowish  brown,  varying  to  a  buff  where  highly  weathered. 
Since  the  drift  is  nowhere  deep  as  compared  with  some  of  the  other 
drifts,  it  is  in  many  places,  leached  and  oxidized  to  the  base.  In 
auger  borings  made  it  was  often  found  that  the  drift  was  leached 
and  oxidized  to  the  bottom.  The  depth  of  leaching  and  oxidation, 
compared  with  the  other  drifts,  is  shown  in  figure  (2).  The  late 
Professor  Calvin  in  speaking  of  the  surface  topography  of  this  drift, 
emphasized  the  importance  of  a  surface  drift  much  as  the  ice  had 
left  it.  So  slight  has  been  the  erosion  that  very  little  trenching  is 


Plate  V. 

Typical   undissected   lowan   drift-plain,   Howard   county.      (Calvin) 

visible  even  along  the  major  water  courses.  Where  streams  have 
gotten  started,  their  valleys  are  but  mere  ditches.  It  has  been 
suggested  that  since  the  lowan  ice-sheet  was  not  a  thick  mass  of 
ice,  it  left  but  a  veneer  of  drift  which  was  not  sufficient  to  oblit- 
erate all  the  irregularities  of  the  o1d  mature  Kansan  surface  over 
wrhich  it  moved.  There  are  within  the  lowan  area  exceptional 
phases  of  topography,  where  the  surface  presents  a  marked  undu- 
latory  effect.  Examples  of  such  areas  may  be  found  in  Butler, 
Bremer,  Black  Hawk,  Howard  and  Mitchell  counties.  Examination 
of  these  areas  shows  them  to  be  hills  of  Kansan  drift,  capped  with 
loess.  If  the  lowan  ice-sheet  was  not  a  vigorous  ice-s'ieet,  it  is 
reasonable  to  assume  that  there  may  have  been  pronounced  rough 
areas  on  the  Kansan  surface,  over  which  the  lowan  ice  was  not  able 
to  pass.  These  areas  are  characterized  generally  by  elliptical  hills 
standing  prominentlv  above  the  level  of  the  surrounding  ground 
moraine  plain.  With  belter  drainage  than  the  ground  moraine 
plain,  after  the  immediate  withdrawal  of  the  ice,  the-e  hills  would 
furnish  favorable  sites  for  the  growth  of  vegetation,  mollusks  would 
find  here  a  suitable  environment  and  become  buried  finally  in  the 
loess.  . 

The  recent  work  of  Alden  and  Leighton  on  the  lowan  drift  calls 
attention  to  the  fact  that,  while  the  general  features  show  an 
erosional  topography,  they  lack  many  of  the  details  characteristic 
of  such  a  surface.  The  valleys  do  not  have  sharp  definition,  but  are 
broad,  round-bottomed  draws  of  dendritic  pattern  having  long, 
smooth  slopes.  In  many  cases  the  heads  and  even  the  slopes  of  the 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  23 

valleys  contain  small  basins  or  ponds.  The  distribution  of  the 
bowlders  suggests  a  promiscuous  mantling  of  the  pre-Iowan  surface, 
in  some  places  sufficient  to  obscure  all  evidences  of  the  old  Kansan 
topography,  while  in  others,  the  mantling  had  the  effect  of  soften- 
ing the  old  Kansan  surface. 


Plate  VI. 

Upper    part    of   plate    shows    lowan    topography    compared    with    the 
Kansan  topography  beneath.      (Alden) 


The  last  ice-sheet  which  invaded  the  state  was  the  Wisconsin. 
This  ice  lobe,  which  had  its  origin  in  the  centers  east  and  west  of 
Hudson  Bay,  entered  the  north  part  of  the  state  between  Clear  Lake 
and  Spirit  Lake,  and  extended  southward  to  and  slightly  beyond 
the  city  of  Des  Moines.  Stratigraphically,  this  drift-sheet  lies  un- 
conformably  upon  the  Kansan  and  Nebraskan,  except  at  its  eastern 
margin,  where  it  is  thought  to  overlap  the  lowan.  Detailed  inves- 
tigation by  the  writer  along  this  eastern  margin,  failed  to  show  a 
single  instance  where  lowan  was  to  be  found  beneath  Wisconsin. 
Numerous  places  were  found  where  it  rests  upon  Kansan  drift. 
It  is  composed  of  clay,  sand,  gravel  and  bowlders.  The  color  differs 
from  all  the  other  drifts.  This  is  due  to  the  fact  that  there  has 
been  little  leaching  and  oxidation  so  that  the  yellowish  brown  and 
reddish  brown  colors  of  the  older  drifts  are  not  to  be  seen  in  the 
Wisconsin  area.  The  prevailing  color  is  light  yellow  where  oxi- 
dized, and  blue  where  unoxidized.  Granite  bowlders  are  present 
but  are  of  darker  color  than  the  lowan  bowlders  and  are,  in  general, 
not  so  large.  While  oxidized  to  an  average  depth  of  three  feet,  it 
is  common  to  find  it  calcareous  to  the  very  surface.  With  the 
exception  of  the  pronounced  terminal  moraine  which  borders  the 
drift,  and  local  recessional  moraines  within  the  outer  border,  the 
Wisconsin  drift-plain  presents  a  level  surface  with  but  slight 
undulations. 


A  STUDY  OF  THE  VARIOUS  DRIFTS 


Plate  VII. 

Typical  Wisconsin   drift-plain,   Kossuth  county,   Iowa.      (Calvin) 

The  plain  is  composed  of  interlocking  and  disconnected,  shal- 
low saucer-like  depressions  with  intervening"  swells  of  slight  convex 
outlines,  hence  it  has  been  designated  frequently  as  the  (?)  "saucer 
type  topography."  The  numerous  basins  vary  greatly  in  shape,  size 
and  depth.  Few  have  outlets  and  where  present,  these  outlets  are 
but  shallow  ditches  through  which  the  water  flows  very  sluggishly. 
Few  streams  are  present  and  where  they  are  found  they  are  always 
of  the  extremely  youthful  type.  The  surface,  as  a  whole,  is  little 
dissected,  is  poorly  drained,  and  is  much  as  the  ice  left  it.  The 
most  marked  topographic  feature  of  the  Wisconsin  plain  is  the 
massive  terminal  moraine  which  borders  it.  This  moraine  stands  as 
a  witness  to  a  vigorous  ice-sheet  that  was  heavily  loaded.  Border- 
ing the  moraine  are  many  excellent  examples  of  kames  and  kame- 
like  eskers,  and  valley  trains,  all  witnessing  to  a  vigorous  outwash 
from  the  edge  of  the  ice. 


BIBLIOGRAPHY. 

1.  B.   Shimek.      The   Nebraskan   drift. 

Science  new  series.  Vol.  34,  1911,  p.  28. 

H.    F.    Bain.      Aftonian    and    pre-Kansan    deposits    in    southern 
Iowa.     American  Geologist,  Vol.  21,   1898,  p.  256. 

2.  A.   C.   Trowbridge.     Geological   work   in   northeast   Iowa. 

Proc.  la.  Acad.  Sciences,  Vol.  21,  1914,  p.  205. 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  25 

3.  B.  Shimek.     Geology  of  Harrison   and  Monona  counties. 

Iowa  Geol.   Surv.  Reports,  Vol.   20,   1909,  p.  307. 

4.  J.    E,    Carman.      Notes    on    the    Nebraskan    drift    of    the    Little 

Sioux    Valley,    Cherokee    county,    Proc.    la.    Acad.    Sciences, 
Vol.  20,   1913,  p.  231. 

5.  G.   F.   Kay.     Pleistocene  deposits  between  Coon  Rapids  in  Car- 

roll   county   and   Manilla   in   Crawford   county.      Iowa   Geol. 
Surv.  Reports,  Vol.  26,   1917,  pp.  230-231. 

6.  S.  Calvin.     Present  phase  of  the  Pleistocene  Problem  in   Iowa. 

Bull.  Geol.  Soc.  America,  Vol.  20,   1909,  pp.   133-152.     , 

7.  S.  Beyer.     Geology  of  Story  county. 

Iowa  Geol.  Surv.  Reports,  Vol.  9,   1898,  p.   199. 


26  CRITERIA  FOR  FIXING  INTERGLACIAL  EPOCHS 

CHAPTER  III. 

THE    INTERGLACIAL    DEPOSITS    OF    IOWA. 
CLASSIFICATION. 

There  are  recognized  in  the  state  five  ice-invasions  and  four 
interglacial  epochs.  The  first  two  interglacial  epochs  are  well 
established  stratigraphically,  while  the  other  three  are  not  so  defi- 
nitely fixed.  The  relation  of  the  drifts  to  the  interglacial  deposits 
is  shown  in  the  following  table. 

The  following  (D  classification  was  used  recently  as  a  report  of 
the  Iowa  Geological  Survey  prepared  in  cooperation  with  the  United 
States  Geological  Survey. 

9.     Wisconsin  drift  (of  the  Des  Moines  lobe) 

8.      (b)    Peorian  soil  and  weathered  zone   (of  Leverett)    at 

top  of  loess  and  beneath  Wisconsin  drift 
(a)    Main  deposit  of  loess 

7.     lowan   drift    (of   Iowa   geologists) 

5.  Sangamon  soil,  vegetal  deposits,  and  weathered  zone 
(of  Leverett)  (including  super-Illinoian  "gumbo," 
or  "gumbotil"  of  Kay)  at  top  of  Illinoian  drift 
and  beneath  loess 

5.     Illinoian   drift    (of  Leverett) 

4.  Yarmouth  soil,  vegetal  deposits,  and  weathered  zone 
(of  Leverett)  (including  super-Kansan  "gumbo,"  or 
"gumbotil"  of  Kay)  at  top  of  Kansan  drift;  also 
Buchanan  gravel  (of  Iowa  geologists)  beneath 
lowan  drift  and  loess 

3.     Kansan  drift  (of  Iowa  geologists) 

2.     Aftonian  gravels,  vegetal  deposits,  soil  and  weathered 
f  zone    (of    Chamberlin)     (including    super-Nebraskan 

"gumbo,"  or  "gumbotil"  of  Kay)    at  top  of  Nebras- 
kan  drift 

i.     Nebraskan    drift    (of    Iowa    geologists)     (pre-Kansan    or    sub- 
(\  J^.  Aftonian  of  Chamberlin) 

If  the  Pleistocene  is  to  be  regarded  as  a  period  it  should  be 
treated  and  analyzed  upon  the  same  basis  as  any  other  division  of 
geological  time.  In  dividing  the  rocks  of  the  earth  into  groups, 
systems  and  series  we  have  used,  (i)  erosional  unconformities,  (2) 
faunal  and  floral  changes,  (3)  physical  changes  and,  (4)  petrological 
and  lithological  differences.  It  is  known  that  the  Pleistocene  is 
set  off  from  the  underlying  formations  by  a  great  unconformity, 
and  is  thus  recognized  as  a  period.  If  it  can  be  shown  that  these 
same  factors  can  be  found  within  the  period  itself,  it  would  seem 
that  there  are  good  reasons  for  dividing  the  Pleistocene  period  into 
Epochs,  the  Epochs  into  Stages  and  the  Stages  into  sub-Stages. 

In  attempting  to  apply  the  above  criteria  to  the  Pleistocene 
great  care  should  be  exercised  as  there  are  places  where  deposits  of 
interglacial  age  cannot  be  interpreted  with  any  degree  of  certainty. 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  27 

It  is  not  easy  to  correlate,   in  age,  deposits  widely  separated. 

The  first  interglacial  epoch,  the  Aftonian,  is  well  established. 
The  factors  which  have  been  used  in  determining  it  are,  (i)  the 
great  erosional  unconformity  between  what  is  known  to  be  older 
drift  and  the  underlying  till-sheet,  (2)  the  presence  of  gumbotil, 
(3)  thick  deposits  of  peat  and  soil  and,  (4)  the  presence  of  faunal 
and  vegetal  remains. 

Recent  investigations  by  Dr.  G.  F.  Kay  have  thrown  much  light 
upon  the  length  of  the  Aftonian  interval.  The  presence  of  a  zone  of 
gumbotil  with  a  maximum  thickness  of  about  thirteen  feet  on  the 
Nebraskan  drift,  where  not  eroded  away,  points  certainly  to  a  long 
time.  Gumbotil,  as  defined  by  Doctor  (2)  Kay.  who  introduced  the 
term,  is  a  gray  to  dark  colored,  thoroughly  leached,  non-laminated 
clay,  deoxidized,  very  sticky,  and  which  breaks  with  a  starch-like 
fracture  when  wet,  which  is  very  hard  and  tenacious  when  dry,  and 
which  is  chiefly  the  result  of  a  long  period  of  weathering  of  drift. 

If  gumbotil  is  the  result  of  thorough  weathering  of  glacial  till 
it  must  be  assumed  that  the  land  remained  in  a  position  such  that 
there  was  little  erosion  during  the  time  of  the  formation  of  the 
gumbotil.  The  leaching  of  drift  is  a  slow  process.  While  the  pro- 
cess of  leaching  and  oxidation  may  be  rapid  at  the  surface,  if  all 
conditions  are  favorable,  these  same  processes  must  be  much  slower 
as  depth  from  the  surface  increases.  Were  it  possible  to  analyze 
all  the  factors  that  affect  the  above  processes,  it  would  be  quite 
probable  that  we  could  get  a  more  definite  estimate  as  to  the  time 
element.  Some  of  the  more  important  factors  that  must  be  consid- 
ered when  an  attempt  is  made  to  interpret  the  problem  of  leaching 
are,  (i)  the  porosity  of  the  drift,  (2)  the  height  of  ground  water, 
(3)  the  amount  of  soluble  matter  in  the  drift  and,  (4)  the  effect  of 
plant  and  animal  life.  Any  attempt  to  make  statements  as  to  the 
time  involved  in  the  leaching  of  a  certain  depth  of  drift  must 
always  be  made  with  the  above  factors  in  mind.  It  would  seem  fair 
to  conclude,  however,  that  if  it  should  take  thousands  of  years  to 
leach  the  upper  two  or  three  feet  of  drift,  it  would  require  many 
times  this  length  of  time  to  leach  and  oxidize  the  next  three  or 
four  feet.  Leaching  of  drift  is  brought  about  chiefly  by  the  perco- 
lating of  meteoric  waters,  but  this  is  a  slow  process,  especially 
where  drift  is  clayey,  since  entering  water  soon  becomes  saturated 
with  mineral  matter,  especially  if  the  drift  is  highly  calcareous. 
Water  once  saturated  will  continue  to  leach  but  very  slowly, 
indeed.  To  leach  drift  to  the  depth  of  15  to  20  feet  must  require 
then  the  gradual  descension  of  the  solution  zone,  a  process  which 
can  never  be  rapid.  As  has  been  shown  bv  (3)  Leighton,  the  rate  of 
descension  of  the  solution  zone  is  probably  greatest  from  the 
surface  down  to  ground  water  level,  for  wet  seasons,  and  less  rapid 
from  this  horizon  to  the  permanent  ground  water  level  where  solu- 
tion becomes  very  nearly  zero.  So  important  is  this  factor  in  deter- 
mining the  depth  of  leaching  and  oxidation  of  drifts,  that  to  over- 
look it.  is  to  give  an  incorrect  interpretation  to  the  fundamental 
facts  of  the  problem  of  oxidation  and  leaching. 

That  the  Aftonian  was  an  epoch  of  great  duration  seems  war- 
ranted from,  (i)  the  thick  layer  of  gumbotil,  an  average  of  13  feet, 
formed  on  the  surface  of  the  old  Nebraskan  drift-plain  and  the 
great  depth  of  oxidized  and  leached  drift  found  beneath  the  gum- 
botil and,  (2)  the  pronounced  erosional  surface  produced  upon  the 


28 


THE  INTERGLACIAL  EPOCHS 


gumbotil-plain    before    the    deposiMon    of    the    subsequent    Kansan 
drift. 

That  the  Aftonian  was  a  true  interglacial  (.])  epoch  is  further 
shown  by  the  occurrence  of  widespread  accumulation  of  peat  and 
soil  zones. 

Large  deposits  of  sand  and  gravel,  which  have  been  called 
Aftonian,  are  found  to  occupy  a  position  between  the  Nebraskan 
and  Kansan  drift-sheets. 


Plate  VIII. 

Deposits  of  Aftonian   gravels   near   Afton   Junction,   Iowa.      (Calvin) 

(5)  The  age  and  mode  of  deposition  of  these  gravels  are  not  yet 
definitely  known.  Recent  work  on  these  gravels  by  Kay  would  seem 
to  indicate  that  they  are  not  interglacial  as  thought  formerly  by 
Shimek  and  others,  but  inclusions  in  the  drift  at  the  time  of  its 
deposition.  The  Aftonian  interglacial  ep^ch  would  seem  to  wrarrant 
the  following  conclusions: — (i)  a  long  time  interval  during  which 
the  Nebraskan  drift  plain  suffered  little  erosion  but  was  undergoing 
marked  chemical  changes  which  resulted  in  the  formation  of  a 
thick  zone  of  gumbotil,  (2)  a  period  of  diastrophism,  as  suggested 
by  Kay,  during  which  there  was  an  elevation  sufficient  to  inaugu- 
rate erosion  and,  (3)  a  long  period  of  erosion  on  the  above  plain. 

The  (6)  Yarmouth  deposits,  representing  the  second  interglacial 
epoch,  were  first  discovered  by  Mr.  Leverett.  A  distinct  peat  and 
soil  zone  was  found  to  occupy  an  intermediate  position  between 
what  was  known  to  be  Kansan  and  a  younger  overlying  drift,  called 
Illinoian.  That  the  Yarmouth  was  a  true  interglacial  epoch  of 
great  duration  has  been  determined  positively  by,  (i)  marked 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA 


29 


physical  changes  which  have  taken  plac3  in  the  Kansan  drift.  The 
surface  of  the  Kansan  CO  drifc,  like  that  of  the  Nebraskan,  is  now 
known  to  have  had  developed  upon  it  gumbotil  to  a  depth  of  20 
feet.  To  produce  such  a  great  thickness  of  gumbotil  must  have 
involved  a  long  time;  (2)  no  interglacial  epoch  has  a  more  marked 
forest  horizon  than  does  the  Yarmouth.  In  the  investigation  car- 
Tied  on  by  the  writer,  scores  of  places  were  found  in  Marshall, 
Hardin,  Franklin,  Cerro  Gordo  and  Worth  counties,  where  vestiges 
of  this  ancient  forest  were  found  to  c  ccupy  a  horizon  that  is  possi- 
bly Yarmouth.  An  excellent  exposure  of  this  old  forest  and  soil 
zone  wras  found  in  Worth  county,  where  the  Wisconsin  drift  lies, 
not  on  lowan,  as  might  be  expected,  but  upon  Kansan  drifc. 


Plate    IX. 

(i)    Wisconsin  drift;    (2)    soil   and  vegetable  zone. 
Soil    and    vegeta'ble    zone    between    Kansan    and    Wisconsin    drifts, 

\\  orth   county. 

The  following  is  a  section  of  the  new  coal  shaft  located  in  the 
N.    W.    l/4    Sec.    6,    Eldora    township,.  Hardin   county,    about    one-half 

mile   northwest   of  the  city. 

Feet.  Inches. 


Black  loamy  soil i 

Yellowish  clay  streaked  with   ferruginous   markings, 

highly  calcareous . 6 

Blue  clay   (probably  Wisconsin)   grades  into   (2)--  12 

Bluish     gray    silt,     non-gritty;     varied     in     thickness 

across  the  shaft;  calcareous 2 


30  THE  INTERGLACIAL  EPOCHS 

5.  Compact    blue    clay,     highly    calcareous    containing 

greenstones,  pebbles  and  pieces  of  limestone 20 

6.  Sand  and  gravel,  mostly  sand,  greenish  blue  in  color     10 

7.  Fine  grained,  flour-like  clay,  greenish  blue 5 

8.  Forest  zone;   well  preserved  limbs,   tree  trunks,   and 
t  branches    were    found    some    of    which    were    in 

situ,  and  as  large  as  six  inches  in  diameter.  In 
every  case  the  vegetal  remains  were  found 
beneath  horizon  (7) 4 

9.  Blue    clay,    highly    calcareous,    the    bottom    part    of 

which  is  black,  as  it  rests  upon  the  shale  over- 
lying the  coal _ Base. 

From  the  relation  of  the  Wisconsin  drift  here  to  the  lowan,  it 
would  seem  that  (4)  is  loess  which  is  abundant  on  the  east  side  of 
the  Iowa  river  bordering  the  lowan  drift.  The  layer  of  bluish 
green  sand  (6)  is  possibly  Yarmouth,  and  (8)  may  be  Aftonian. 

The  following  is  a  type  section  in  Story  county,  Section  12,  T. 
82  N.  Range,  21,  W. 

Feet.  Inches. 

1.  Black  soil i 

2.  Muck  and  peat 2  3 

3.  Kansan     gumbotil 3 

Here  Wisconsin  drift  rests  upon  a  peat  and  muck  zone  which 
represents  the  time  between  the  deposition  of  the  Kansan,  the  for- 
mation of  the  gumbotil,  the  deposition  of  the  peat  and  muck,  and 
the  coming  of  the  Wisconsin  ice-sheet.  A  study  of  the  amount  of 
erosion  shown  by  the  Kansan  drift  leads  to  the  conclusion  that  this 
interval  must  have  been  long,  for  in  many  cases  the  streams  have 
removed  the  entire  thickness  of  (8)  gumbotil. 

The  term  Sangamon  was  first  used  by  (9)  Leverett,  and  was  applied 
to  a  peat  and  soil  formation  lying  above  Illinoian  drift  and  beneath 
loess  which  was  thought  to  be  of  lowan  age.  That  the  Sangamon 
epoch  was  a  true  interglacial  epoch  is  shown  by,  (T)  the  presence 
of  a  layer  of  gumbotil  covering  the  Illinoian  to  a  depth  of  5  feet  or 
more,  (2)  marked  erosion  of  the  gumbotil-plain,  (3)  the  presence 
of  thick  peat  and  soil  zones  and,  (4)  the  presence  of  fossil  insect 
life. 

The  last  interglacial  epoch,  the  (10)  Peorian,  represents  the  time 
between  the  retreat  of  the  lowan  ice  and  the  coming  of  the  Wis- 
consin. In  no  place  has  Wisconsin  drift  been  found  to  overlie  the 
uneroded  lowan.  Such  a  place  would  be  ideal  for  the  study  of  the 
Peorian  interglacial  epoch.  While  peat  and  soil  zones  have  been 
reported  to  underlie  the  Wisconsin  in  McHenry,  Kane,  DeKalb  and 
Bureau  counties,  Illinois,  by  Mr.  (U)  Leverett,  there  is  no  evidence 
that  the  drift  underlying  the  peat  and  muck  is  lowan  drift.  More 
recent  work  on  the  drift  in  (12)  Illinois,  since  the  writing  of  Mr.  Lev- 
erett's  Monograph,  has  reduced  greatly  the  area  of  distribution  of 
the  I!owan  drift.  The  only  place  where  the  lowan  drift  appears  to 
have  crossed  the  Mississippi  (13)  river,  and  this  is  probably  question- 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  31 

able,   was    the    northwestern    and   west    central    part   of   Rock   Island 
and  Whiteside  counties,   Illinois. 

The  Toronto  (14)  beds  of  Ontario,  Canada,  were  thought  by  Pro- 
fessor Chamberlin  to  be  Peorian  in  age,  but  there  is  some  doubt  as 
to  whether  these  beds  should  be  classed  as  Peorian  or  Sangamon. 
Recent  investigation  would  seem  to  favor  placing  these  beds  as 
Sangamon  in  age.  The  only  deposits  that  are  now  known  to  be 
definitely  of  Peorian  age  are  the  loess  deposits,  which  will  be  dis- 
cussed in  another  connection  in  this  report. 


BIBLIOGRAPHY. 


1.  Classification   of   the   Pleistocene   of   Iowa  made    in   cooperation 

with    the   United    States   Geological    Survey,    la.    Geol.    Surv. 
Reports,  Vol.  26,  1915,  pp.  56-57. 

2.  G.   F.    Kay.        Gumbotil,    a   new    term    in     Pleistocene     Geology. 

Science  Vol.  44,   1916,  p.  637. 

The  Origin  of  Gumbotil.     Jour,  of  Geology,  Vol.   28,   No.   2, 

1920. 

3.  M.  M.  Leighton.     Leaching  of  the  Pleistocene  drifts  of  eastern 

Iowa.     Proc.  la.  Acad.  Sciences,  Vol.  22,   1915,  p.   19. 

4.  G.  E.   Finch.       Drift  section  at  Oelwein,   Iowa.     Proc.  la.  Acad. 

Sciences,  Vol.  4,   1897,  p.   54. 

S.  Calvin.  Geology  of  Chickasaw  county,  la.  Geol.  Survey 
Reports,  Vol.  13,  1902,  p.  281. 

5.  H.  F.  Bain.     Aftonian  and  pre-Kansan  deposits  in  southwestern 

Iowa.     American   Geologist,   Vol.    21,    1898,   p.    255. 

G.  F.  Kay.  The  Aftonian  gravels  near  Afton  Junction — are 
they  interglacial?  Proc.  la.  Acad.  Sciences,  Vol.  26,  1919. 

S.  Calvin.  Aftonian  gravels  and  their  relations  to  drift-sheets 
in  -regions  about  Afton  Junction  and  Thayer.  Proc.  Daven- 
port Acad.  Sciences,  Vol.  10,  1907,  p.  18. 

B.  Shimek.  Aftonian  sands  and  gravels  in  western  Iowa.  Sci- 
ence new  series,  Vol.  28,  1908,  p.  923. 

6.  F.    Leverett.      Weathered    zone    (Yarmouth)    between    the    Illi- 

noian  and  the  Kansan  till-sheets.     Proc.  la.  Acad.  Sciences, 
Vol.  5,  ,1898,  p.  81. 

7.  G.    F.    Kay.      Some    features    of    the    Kansan    drift    in    southern 

Iowa.       Bulletin     Geol.     Soc.     America,     Vol.     27,     1916,     pp. 
115-117. 

8.  G.    F.    Kay.      Some    evidences    regarding    the    duration    of    the 

Yarmouth  interglacial  epoch.     Science,  Vol.  43,   1916,  p.  398. 

9.  F.  Leverett.     Weathered  zone  (Sangamon)  between  lowan  loess 

and    Illinoian    till-sheet.      Proc.    la.    Acad.    Sciences,    Vol.    5, 
1898,  pp.  71-80.     Jour,  of  Geology,  Vol.  6,   1898,  pp.   171-181. 


32  BIBLIOGRAPHY 

10.  F.    Leverett.      The    Peorian    soil    and    weathered    zone    (Toronto 

formation).     Monograph  U.  S.  Geol.  Survey,  Vol.  38,  1899,  p. 
185. 

11.  F.    Leverett.      The    Peorian    soil    and    weathered    zone    (Toronto 

formation).     Monograph  U.  S.  Geol.  Survey,  Vol.  38,  1899,  p. 
185. 

12.  H.   H.   Barrows.      Geography  of   the   middle   Illinois  valley.      111. 

Geol.   Survey  Bulletin   No.    15,    1910,   p.   31. 

13.  J.    E.    Carman.      The    Mississippi   valley   between   Savannah    and 

Davenport.      111.    Geol.    Survey    Bulletin,    No.    13,    1909,    pp. 
40-41. 

14.  A.    P.    Coleman.        Glacial    and    interglacial   beds   near   Toronto. 

Jour,  of  Geology,  Vol.  9,   1901,  p.  285. 


'f 
SOME  PHASES  OF  THE  PLEISTOCENE  O'F  IOWA  33 

CHAPTER  IV. 
THE  LOESS. 

Since  the  loess  has  such  an  important  bearing  upon  the  prob- 
lem of  the  Peorian  interglacial  epoch  it  will  be  necessary  to  review 
briefly  the  early  history  of  investigation  of  loess,  especially  in 
Iowa. 

Loess  was  recognized  and  brought  into  prominence  first  by 
German  geologists.  It  wras  in  the  valley  of  the  Rhine,  where  for  a 
long  time  the  term  loess  had  'been  in  common  usage  by  the 
peasants,  that  the  term  as  it  is  now  known,  had  its  origin.  After 
its  discovery  in  Germany,  it  was  not  long  until  it  was  recognized  in 
other  localities  of  Europe  and  even  in  Asia  and  America.  It  was 
observed  in  this  country  first  by  Sir  Chas.  Lyell.  During  his  second 
visit  to  this  country,  in  1846,  he  recognized  along  the  lower  portion 
of  the  Mississippi  river  valley,  in  the  vicinity  of  New  Orleans,  a 
deposit  of  loam-like  material  mantling  the  bluffs,  which  he  believed 
compared  very  favorably  with  the  loess  found  in  the  valleys  of  the 
Rhine  and  Danube.  After  having  made  a  careful  examination  and 
analysis  of  its  fossil  life,  he  pronounced  it  loess,  and  gave  as  his 
theory  of  genesis,  "the  flood-theory  of  the  Mississippi  river,"  which 
theory  was  accepted  by  many  American  geologists  until  the  time  of 
Richthofen's  work  on  the  loess  in  China. 

In  Iowa,  loess  was  first  discovered  along  the  Des  Moines  and 
Missouri  rivers  by  (1)  D.  D.  Owen  who  characterized  it  as  siliceous 
marl.  He  explained  its  presence  along  the  Missouri  river  by  the 
fact  that  the  waters  of  the  Missouri  river  had  at  some  time,  conse- 
quent to  the  drift  period,  been  dammed  making  a  vast  inland  lake, 
into  which  was  carried  a  fine,  lacustrine-like  sediment  which  en- 
tombed fresh  water  and  terrestrial  forms  of  shell  life. 

As  early  as  1868,  (2)  W.  H,  Pratt  of  Davenport,  made  a  very  careful 
study  of  the  loess  within  the  vicinity  of  the  city.  He  described  it 
as  a  yellowish  clay  in  which  the  lines  of  stratification  consisted 
principally  of  iron  stained  streaks  and  occasional  thin  layers  of 
sand.  The  whole  presents  a  distinctly  laminated  structure.  In 
certain  portions  of  the  deposit  many  calcareous  concretions  are  to 
be  seen,  which,  in  almost  every  respect,  correspond  to  those 
described  by  Lyell  from  the  Rhine  valley  loess.  So  firmly  did  he 
believe  the  Mississippi  loess  to  be  analogous  to  the  loess  of  the 
Rhine  valley  that  he  spoke  of  it  as  having  the  same  characters. 
From  the  presence  of  so  many  fragile,  unbroken  fossil  remains, 
and  the  apparently  horizontal  laminations,  he  reasoned  that  the 
entire  body  pf  the  loess  must  have  been  deposited  in  comparatively 
quiet  bodies  of  water. 

In  1878,  (3)  C.  A.  White  re-examined  the  loess  along  the  Missouri 
river  and  gave  to  it  the  name  "Bluff  Loess,"  a  term  which  had  been 
adopted  by  the  Missouri  geologists.  He  interpreted  its  genesis 
somewhat  differently  from  those  who  had  preceded  him.  He  be- 
lieved the  material  to  have  been  obtained  from  the  Tertiary  and 
Cretacecus  formations  of  the  upper  Missouri  river.  This  material 
was  washed  down  and  deposited  in  large  inland  lakes  which  were 
formed  subsequent  to  the  close  of  the  glacial  period. 

In  1878,  (4)  J.  E.  Todd  again  investigated  the  loess  deposits  of 
southwestern  Iowa  and  contrasted  them  in  an  analytical  way  with 
the  loess  of  China,  which  had  been  described  by  Baron  Richthofen. 


34  EARLY  WORKERS  ON  THE  LOESS  OF  IOWA 

In  writing  of  the  loess  he  says  "the  description  of  the  Chinese  loess 
might  readily  be  applied  to  pur  southwestern  deposits.  The  same 
language  might  be  used  word  for  word,  except  that  a  few  diminu- 
tives must  be  thrown  in  when  altitudes  are  referred  to.  We  have 
the  same  surface  features,  the  same  minute  vertical  tubes  inter- 
joining  at  acute  angles,  the  same  absence  of  stratification,  the  same 
vertical  underdrainage  and  cleavage,  the  same  line  of  calcareous 
concretions,  which  line  is  usually  horizontal,  the  same  yellow  earth, 
and  lastly  the  Missouri,  or  "Muddy  river,"  which  is  the  close 
counterpart  of  the  Hoang-Ho,  or  "Yellow  river."  Professor  Todd 
found  upon  closer  investigation  serious  objections  to  the  Richthofen 
theory  in  the  presence  of,  (i)  aquatic  shell  life,  as  he  then  inter- 
preted it,  (2)  evidence  of  distinct  lamination  and,  (3)  the  constant, 
almost  uniform,  thickness  of  the  loess  on  the  hill  tops  and  hillsides. 
This  peculiar  distribution  is  explained  in  that,  subsequent  to  the 
glacial  period,  the  Missouri  river  became  dammed  somewhere  to 
the  south,  forming  a  large  inland  lake.  Into  this  lake,  sediment 
was  carried  and  deposited  uniformly  over  the  entire  bottom.  Owing 
to  a  complete  drainage  of  the  lake,  before  the  inequalities  of  the 
bottom  had  been  levelled  up  by  the  complete  filling  of  the  lake  to 
water  level,  the  material  was  left  at  the  various  altitudes  at  which 
it  is  now  found. 

(5)  R.  E.  Call,  writing  of  the  loess  in  1882,  referred  to  it  as  being 
limited,  for  the  most  part,  to  the  extreme  western  and  southwestern 
part  of  the  state.     In   a  later  article,   he  speaks  of  finding  loess  in 
the  vicinity  of  Des  Moines,  situated  beneath  the  drift  of  the  last  ice- 
sheet,    and   makes   the   following   interesting   remark: — "It    has   been 
thought   best   to   record  simply   the   finding  of  it   here   and   leave   to 
others  the  forming  of  any  theory  as  to  its  mode  of  origin."     After 
studying  critically   the    fossil    life   of   the   loess   in    this   vicinity,    he 
classified  it  as  either  aquatic,  semi-aquatic  or  lacustrine,   and  in  so 
doing,    held    analogous   views    to    those    of   Professor   Todd   as    to    its 
genesis.     The   small   size   of  the   fossil   shell   life   he   attributed   to   a 
pauperitic  fauna  which  must  have  resulted  from  the  severe  temper- 
ature conditions  of  the  glacial  waters. 

(6)  F.  N.  Witter,  Superintendent  of  Muscatine  Public  Schools,  early 
became  interested  in  the  loess  deposits  found  on  the  bluffs  border- 
ing the  city.     He  had  observed  that  the  loess  rested  on  glacial  drift, 
and    that    a   part    of   it   was    stratified.      In    the    underlying    drift    he 
found   bowlders,   coarse   gravel,    sand    and  clay,    and    above,    without 
any  sharp  line  of  demarcation,   rested  the  loess  which   expended   to 
the    top    of    the    highest    hill.      It   was   observed    that    the    color   was 
yellowish  to  ashy,  that  stratification  lines,  though  present  in  places, 
were    in    other    places    absent,    and    that    scattered    throughout    the 
mass,   were   stony  concretions  of  very   irregular   form.     Large   num- 
bers of  land  snails,  most  perfectly  preserved,  were  found  in  all  parts 
of   the  loess,    except   near   the   base.     Since   stratification   lines  were 
generally  absent,  Mr.  Witter  was  convinced  that  the  material  never 
could  have  been   deposited  by  currents  of  water.     It  was  his  belief 
that  deposition   took  place  in   a  large  lake,   the  bed  of  which  must 
have  been   subjected   to   little  or  no  change   during  the   time   of  its 
deposition. 

(8)  W  J  McGee,  during  the  time  of  his  association  with  the 
Archaeological  Reconnaisance  work,  made  his  headquarters  at 
Farley,  Iowa.  It  was  while  a  member  of  this  organization  that  he 
became  interested  in  the  drift  deposits  of  northeastern  Iowa.  Hav- 


SOME   PHASES  OF  THE  PLEISTOCENE  OF   IOWA  35 

ing  made  a  careful  study  of  the  loess,  he  divided  the  northeastern 
region  into  three  distinct  areas,  namely,  (i)  the  northern  loess, 
(2)  the  bluff  and  paha  area  and,  (3)  the  southern  loess. 

The  northern  area  included  the  driftless  region,  as  then 
known,  and  its  southern  flanks,  comprising  roughly  the  area  from 
the  Mississippi  river  westward  to  the  head  waters  of  the  Turkey, 
Volga  and  North  Maquoketa,  in  eastern  Jackson  and  northern  Clin- 
ton counties,  and  thence  to  the  eastern  part  of  the  territory.  With- 
in this  area  the  loess  was  noted  for,  (i)  its  striking  inability  to 
stand  for  any  length  of  time  in  steep  slopes  as  shown  by  the  loess 
further  to  the  south,  (2)  its  approximate  homogeneity  from  summit 
to  base  where  it  was  found  to  pass  almost  universally  into  a  sheet 
of  sand  and  gravel  and  bowlder-charged  clay,  (3)  its  universal 
mantling  of  the  "Driftless  Area"  though  it  became  very  thin  and 
rather  inconspicuous,  especially  on  the  divides,  where  it  is  made  up 
largely  of  the  local  material,  so  that  it  becomes  difficult  often  to 
tell  it  from  the  residuary  clays,  (4)  its  overlapping  of  the  drift 
margin  for  great  distances,  (5)  its  marked  hypsometric  distribution, 
being  as  great  as  the  relief  of  the  region  in  which  it  is  found,  (6) 
its  variability  in  thickness  from  the  north  to  the  south  and  from 
the  Mississippi  river  to  its  southern  margin,  (7)  its  prevailing  light 
drab  color  above,  with  a  grading  into  a  bluish  gray  below,  (8)  the 
wide,  universal  distribution  of  fossil  shells,  and  more  commonly  in 
the  bluish  loess,  (9)  the  presence  of  irregular  cylindrical-like  con- 
cretions in  the  upper  part  of  the  loess,  (10)  the  lack  of  stratification 
lines,  except  in  the  basal  portions  of  a  few  localities  and  high  level 
terraces,  (n)  the  presence  of  a  pebble  bed  at  the  base  into  which 
the  loess  grades,  sometimes  slowly,  at  other  times  rapidly,  (12)  the 
greater  abundance  of  loess  shells  in  the  southern  portion  of  the 
area  than  in  the  northern  and,  (13)  the  predominance  of  a  more  or 
less  pauperitic  fauna  in  the  south. 

The  loess  of  the  river  and  paha  phase  extends  over  a  larger 
area  which  lies  somewhat  to  the  west  of  the  first  area  above 
described,  and  extends  to  the  Iowa-Cedar  divide  in  Marshall  county. 
From  here  the  line  crosses  the  Iowa  river  in  northern  Johnson 
county  and  then  extends  on  east  to  a  line  connecting  the  great 
elbow  of  the  Cedar  river  with  the  Wapsipinicon  river.  Within  this 
area  the  loess  was  noted  for,  (i)  its  tendency  to  arrange  itcelf  in 
lines  or  belts  which  are  more  or  less  roughly  parallel  with  the 
water  courses,  (2)  its  increasing  tendency,  especially  in  the  south- 
east, to  become  more  homogeneous  and  fossiliferous,  (3)  its  rather 
close  blending,  toward  its  southern  margin,  with  the  underlying 
drift  material,  (4)  its  universal  capping  of  the  summits  of  the 
pahas  and  ridges  through  which  the  streams  had  often  cut  gorges, 
(5)  the  tendency  to  mantle  high  northern  banks  of  aberrant  stream 
tributaries  and,  (6)  its  marked  continuity  in  passing  from  higher 
to  lower  levels. 

The  region  of  the  southern  loess  described  by  McGee  lay  to  the 
south  of  the  river  and  paha  phase  and  extended  from  the  southeast 
corner  of  the  above  area  to  the  Mississippi  river  in  Muscatine  and 
Scott  counties.  The  loess  here  was  noted  to  contain  abundant  fos- 
sils, loess  kindchen,  iron  tubules  and  to  be  continuous  from  one 
level  to  another.  Unlike  the  northern  loess,  however,  it  thinned 
away  from  the  streams  and  passed  into  the  underlying  drift  so 
gradually  that  it  becomes  very  difficult  to  tell  just  where  the  loess 
ceases  and  the  drift '  commences.  Because  of  this  latter  striking 
peculiarity,  McGee  thought  his  southern  loess  a  sort  of  connecting 


36  EARLY  WORKERS  ON  THE  LOESS  OF  IOWA 

link,  not  only  between  divergent  phases  of  the  deposit,  but  between 
the  deposit  itself  and  one  commonly  regarded  as  distinct  in  genesis 
and  period  of  formation,  hence  his  name  of  "hybrid  loess."  He  was 
strongly  convinced  that  the  origin  of  the  loess  was  associated  with 
glacio-fluvial  waters. 

The  most  noted  and  detailed  early  work  on  the  loess  was  the 
investigation  by  (8)  T.  C.  Chamberlin  and  R.  S.  Salisbury.  Their 
report  of  the  loess  of  the  "Driftless  Area"  is  one  of  the  classics  in 
geological  literature.  An  attempt  is  made  to  analyze  the  loess  as 
to  its  composition  and  physical  properties.  Their  earlier  inter- 
pretation regarding  the  genesis  of  the  loess  has  within  recent  times 
been  modified  so  as  to  include  the  work  of  the  winds  as  well  as  the 
work  of  glacial  waters. 

In  the  more  recent  investigations  of  the  loess,  the  work  of  no 
one  man  stands  out  more  prominently  than  that  of  Professor 
Shimek,  of  the  State  University  of  Iowa.  His  study  of  the  loess  has 
extended  over  a  period  of  more  than  a  quarter  of  a  century.  He 
first  became  interested  in  the  loess  through  the  study  of  soils  in 
relation  to  plant  ecology.  Soils  have  much  to  do  with  providing  a 
suitable  environment  for  plant  growth,  as  well  as  providing  a  feed- 
ing ground  for  molluscan  life.  It  was  from  this  viewpoint  that 
Professor  Shimek  began  his  intensive  study  of  the  loess.  After 
having  made  a  most  careful  investigation  of  the  loess  within  the 
state,  he  began  the  study  of  the  loess  deposits  of  other  localities 
without  the  state.  After  having  made  a  careful  study  of  all  the 
various  theories  that  have  been  advanced  to  account  for  the  origin 
of  loess  and  its  distribution,  he  was  convinced  that  no  other  theory 
could  account  for  all  the  difficulties  so  well  as  the  eolian  theory. 
The  facts  that  any  theory  must  answer  are,  (i)  the  presence  of 
terrestrial  mollusks,  (2)  the  hypsometric  and  geographic  distribu- 
tion, (3)  the  absence  of  stratification  lines  but  the  presence  of 
lamination,  (4)  the  absence  of  aquatic  shell  life  and,  (5)  the  rela- 
tion to  the  drift-sheets. 

As  early  as  1888,  Professor  Shimek  published  a  list  of  the  fossils 
which  he  found  in  the  loess  around  Iowa  City,  and  showed  most 
conclusively,  that  the  fossils  of  the  loess  are  not  aquatic,  but  on 
the  other  hand,  are  terrestrial  almost  without  exception.  He  has 
called  attention  further  to  the  fact,  that  there  is  a  marsh  fauna 
and  a  pond  fauna  which  lives  in  or  near  small  pools  of  water,  but 
this  fauna  is  not  to  be  considered  as  aquatic,  since  by  its  organiza- 
tion it  is  proven  that  it  could  not  live  in  the  water.  He  has  shown 
also  that  habitat  determined  largely  the  grouping  of  the  mollusks, 
each  species  when  living,  demanding  different  environment  from 
other  species.  The  differences  are  due  not  so  much  to  temperature 
as  to  the  moisture  conditions.  This  explains  easily  the  difficulty 
that  R.  E.  Call  and  W  J  McGee  found  in  trying  to  account  for  the 
small  shell  life  of  the  loess  in  the  vicinity  of  Des  Moines.  By 
making  a  comparison  of  the  present  life,  in  any  region  investigated, 
with  th^e  fossil  life  of  the  same  locality  today,  Professor  Shimek 
has  proven  beyond  doubt,  that  the  climate  during  which  the  shell 
life  of  the  loess  was  entombed,  was  much  the  same  as  the  climate 
of  those  same  regions  today,  and  that  there  are  very  few,  if  any, 
differences  in  the  species  that  were  living  in  these  same  regions 
when  they  were  buried  in  the  loess.  It  may  be  said  with  safety 
that  the  eolian  theory  has  now  become  the  generally  accepted 
theory  for  the  loess  distribution. 

The  names  of  many  other  men  who  have  made  some  study  of 
the  loess  might  be  mentioned.  Some  of  the  more  prominent  are 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  37 

S.  Calvin,  T.  E,  Savage,  H.  F.  Bain,  A.  G.  Leonard,  W.  H.  Norton, 
and  S.  Beyer. 

The  most  important  theories  that  have  been  advanced  to 
account  for  the  loess  and  its  distribution  are,  (i)  the  lacustrine 
theory  which  ran  through  many  forms,  from  a  semi-marine  or  estu- 
arine  on  the  one  hand,  to  the  forming'  of  large  inland  lakes  by  the 
damming  of  rivers  on  the  other,  (2)  the  fluviatile  theory  which 
assumed  that  the  loess  is  more  or  less  associated  with  running 
water,  (3)  the  glacio-fluvial  theory  which  assumed  that  at  the 
maximum  extent  of  the  ice,  numerous  shallow  lakes  were  formed 
on  the  surface  immediately  in  front  of  the  ice  into  which  the 
streams,  issuing  from  the  glacier  front,  deposited  their  loads  of  fine 
material,  (4)  glacio-eolian  which  differed  from  (3)  in  that,  after 
deposition  of  the  material  by  glacial  streams,  the  wind  played  an 
important  part  in  its  distribution  and,  (5)  the  eolian  theory  which 
makes  the  agent  of  distribution  the  wind. 

While  there  is  quite  general  agreement  regarding  the  genesis 
and  mode  of  distribution  of  the  loess,  there  are  still  differences  of 
opinion  as  to  its  age.  There  are  those  who  would  make  the  main 
body  of  loess  lowan  or  immediately  post-Iowan,  while  still  others 
would  make  the  loess  of  two  distinct  ages,  or  even  more.  Since  the 
age  of  the  loess  is  important  in  relation  to  the  Peorian  interglacial 
epoch  the  views  of  some  of  the  more  noted  workers  regarding  the 
age  of  the  loess  will  be  given. 

B.  Shimek  in  speaking  of  the  age  of  the  loess  says  (9)  "there  is  at 
present  no  warrant  whatever  for  the  reference  of  all  loess,  and 
especially  that  of  the  Missouri  river,  to  lowan  age.  A  thin  layer  of 
loess  is  found  over  a  part  of  the  lowan  and  Wisconsin  and  no 
connection  has  yet  been  established  between  the  lowan  and  the 
loess  of  the  Missouri  and  Big  Sioux  rivers.  It  is  known  that  loess 
in  northwestern  Iowa  belongs  probably  to  more  than  one  glacial 
epoch,  and  Professor  Macbride's  work  in  Humboldt  county,  makes  it 
conclusive  that  the  lowan  did  not  cover  the  region  immediately 
north  of  Carroll  county  as  heretofore  believed.  The  correlation  of 
the  loess  in  Carroll  county  with  the  lowan  drift  is  accordingly  open 
to  considerable  doubt.  Differences  in  composition  and  texture  may 
frequently  be  observed  in  the  loess  which  make  it  evident  that  not 
all  loess  is  of  the  same  age  as  measured  with  reference  to  the  sev- 
eral drift-sheets  which  have  extended  southward  into  the  latitude 
of  Iowa.  The  (10)  deposition  of  the  loess  has  continued  through  all  the 
intervals  of  the  ice  age,  though  in  more  northerly  regions,  over 
which  the  several  ice-sheets  passed,  there  are  more  or  less  sharply 
defined  differences  between  different  portions  of  the  loess.  The 
reference  of  the  loess  to  any  one  drift  epoch  must  be  objected  to, 
and  not  the,  least,  on  account  of  frequent  presence  of  numerous 
land  snails  which  indicate  also  the  existence  of  a  vigorous  vegeta- 
tion. The  several  loesses  represent  interglacial  and  post-glacial 
epochs  during  which  conditions  could  not  have  been  materially 
different  from  now." 

Prof.  (ID  S.  Calvin  in  discussing  the  loess  of  northeastern  Iowa, 
contended  that  the  main  portion  of  it  was  a  silt  derived  from  the 
finer  materials  of  the  lowan  drift.  This  was  shown  to  be  true  by 
its  color,  composition,  its  geographical  relation  to  the  margin  of 
the  lowan  drift,  and  by  its  superposition,  sometimes  on  the  lowan 
till  and  as  often  on  an  eroded  and  oxidized  surface  of  the  Kansan. 
In  his  work  in  (12)  Howard  county,  Professor  Calvin  calls  attention  to 
the  fact  that  here,  as  well  as  in  Mitchell  and  other  counties,  there 


38  THE  AGE  OF  THE  LOESS 

is  a  thin  veneer  of  loess  that  is  younger  than  the  lowan  and  is 
probably  of  Wisconsin  age.  In  Winneshiek  county,  Professor 
Calvin  calls  attention  to  two  distinct  loesses  which  are  quite  widely 
distributed  throughout  the  county.  He  makes  the  older  loess  close- 
ly related  to  the  Kansan  drift-sheet,  while  the  upper  and  younger 
he  calls  lowan.  Observations  on  the  loess  near  Peoria,  Illinois,  led 
to  the  conclusion  that  here  the  loess  is  as  strongly  developed  as  it 
is  on  the  lowan  in  Howard  county.  In  his  (13)  Presidential  Address 
before  the  Geological  Society  of  America,  in  1909,  Professor  Calvin 
states  that  the  loess  of  certain  parts  of  the  Mississippi  valley  be- 
longs to  the  interglacial  epoch  between  the  lowan  and  the  Wiscon- 
sin. 

Prof.  (14)  H.  W.  Norton  in  discussing  the  loess  of  the  Kansan  areas 
that  are  found  within  the  lowan  in  Bremer  county,  reaches  the 
conclusion,  though  both  gray  and  yellow  loess  are  present,  that  the 
loess  is  decidedly  younger  than  the  Kansan  and  apparently  is  lowan 
in  age. 

Prof.  (15)  J.  L.  Tilton  in  his  report  on  the  geology  of  Warren 
county,  suggests  the  possibility  of  more  than  one  loess.  He  takes 
as  his  type  section  the  exposure  at  the  Indianola  Brick  and  Tile 
Company's  plant,  situated  to  the  north  of  the  city.  Here  the  upper 
loess,  about  5  feet  thick,  is  fossiliferous,  appears  darker  and  is  more 
clayey.  The  line  of  separation  between  the  two  is  more  or  less 
sinuous,  suggesting  a  possible  downward  limit  to  oxidation,  or  a 
disturbed  surface  upon  which  the  loess  was  deposited.  The  lower 
and  darker  loess  may  have  been  derived  from  the  Kansan  drift. 

Prof.  (16)  R.  S.  Salisbury  reports  loess  of  Wisconsin  age  in  the 
vicinity  of  Green  Lake  county,  Wisconsin,  to  the  east  of  the  south 
end  of  Devil's  Lake,  and  again  at  Ableman's  in  the  same  vicinity. 
In  the  former  exposure,  loess  is  found  at  an  elevation  of  150  to  200 
feet  above  the  level  of  the  lake  and  lying  on  Wisconsin  till.  Here 
the  loess  is  not  fossiliferous  nor  does  it  contain  the  loess  kindchen. 
A  second  exposure  in  the  vicinity  of  the  same  lake  was  found  at  a 
much  lower  level,  was  thicker,  fossiliferous,  more  normal  in  color 
and  texture  and  contained  concretions.  At  Devil's  Lake  the  loess 
was  found  directly  associated  with  the  Wisconsin  terminal  moraine. 
Here  the  moraine  is  at  an  elevation  of  60  to  80  feet  above  the  lake 
level,  and  on  the  side  facing  the  lake,  the  loess  is  associated  with 
fine  clay  which  suggests  that  it  was  accumulated  in  the  expanded 
lake  which  occupied  the  present  lake  and  its  surroundings  at  the 
time  of  the  ice  occupancy.  The  loess  here  is,  no  doubt,  the  fine 
sediment'  that  settled  from  the  muddy  waters  of  the  lake  which 
stood  here  for  some  time  after  the  ice  had  withdrawn  some  distance 
to  the  east.  The  exposure  at  Ableman's  is  not  associated  with  any 
of  the  older  drift-sheets.  It  occurs  at  a  very  low  elevation  on  a 
lacustrine  flat  made  by  a  lake  which  formerly  occupied  the  valley 
of  the  Baraboo  river  just  'above  the  city  of  Baraboo,  during  the 
time  that  the  ice  blocked  the  eastern  drainage  of  the  valley.  This 
lake  was  maintained  sometime  after  the  retreat  of  the  ice  by  a 
moraine  dam.  On  this  flat  the  loess  was  deposited  probably  by 
glacial  waters.  It  is  reported  also  that  loess-like  loam  is  present  on 
the  low  plain  about  Camp  Douglas.  It  is  possible  that  the  loam- 
like  material  was  deposited  by  the  flood  waters  associated  with  the 
Wisconsin  ice-sheet. 

In  describing  the  deposits  of  Crowley's  Ridge,  Professor  (17)  Salis- 
bury refers  the  loess  to  two  distinct  epochs;  the  first  deposition 
followed  the  first  glacial  episode,  which  is  to  be  interpreted  as 


SOME  PHASES  OF  THE  PLEISTOCENE,  OF  IOWA  39 

Kansan;  the  second  epoch  of  deposition  followed  the  episode  which 
corresponds  to  the  lowan. 

Prof.  (18)  J.  A.  Udden  reported  a  fossiliferous  loess-like  clay  from  a 
well,  located  in  the  city  of  Moline,  Illinois.  The  well  is  located  on 
the  Mississippi  bottom,  and  the  loess-like  silt  was  penetrated  at  a 
depth  of  30  feet.  The  upper  clay  is  interpreted  to  be  Illinoian 
drift.  Whether  these  deposits  are  extra-glacial  deposits,  made  in  a 
lake  in  front  of  an  advancing  ice-sheet,  or  are  material  like  the 
surface  loess,  remains  to  be  determined. 

Prof.  (19)  C.  W.  Wilcox  of  Ames,  Iowa,  in  describing  some  loess 
deposits  of  southwest  Iowa,  calls  attention  to  the  occurrence  of  a 
red,  a  white  and  a  yellow  loess,  and  suggests  that  they  cannot  be 
different  phases  of  one  original  loess  which  has  undergone  second- 
ary modification  produced  by  weathering  and  interstitial  deposition 
of  material  by  infiltration. 

It  has  been  suggested  that  McGee  had  in  mind  two  distinct 
loess-making  periods.  A  careful  study  of  the  literature  which  has 
to  do  with  the  work  of  McGee  on  the  loess,  fails  to  reveal  any 
specific  statement  to  more  than  one  loess.  It  is  of  interest  to  note 
that,  after  having  studied  the  loess  in  the  vicinity  of  Des  Moines, 
he  made  note  of  the  fact  that  the  loess  was  overlain  by  drift,  while 
beneath,  it  graded  into  drift,  and  that  midway  between  Des  Moines 
and  the  Mississippi  river,  especially  in  the  southern  part  of  the 
state,  it  merged  into  the  underlying  drift  so  gradually  that  no 
sharp  line  of  division  between  the  two  could  be  drawn. 

Mr.  (20)  W.  H.  Pratt,  in  his  report  of  the  loess  of  Davenport  and 
vicinity,  makes  reference  to  a  loess  that  in  the  lower  part  was 
bluish  gray,  and  ^in  the  upper  part  was  yellowish,  but  makes  no 
definite  reference  to  the  age. 

Mr.  (21)  H.  F.  Bain,  in  his  report  of  the  Geology  of  Carroll  county, 
was  of  the  opinion  that  the  age  of  the  loess  could  not  be  positively 
fixed.  In  eastern  Iowa  and  Illinois  the  bulk  of  the  loess  seems  to 
have  been  deposited  contemporaneously  with  the  maximum  advance 
of  the  lowan  ice,  but  the  loess  in  northwestern  Iowa  belongs  to 
more  than  one  ice  epoch.  Since  the  lowan  ice  did  not  reach  this 
far  west  any  attempt  to  associate  it  with  the  lowan  drift  is  open  to 
some  doubt. 

Prof.  (22)  T.  O.  Maybray,  in  writing  of  the  loess  said  "the  loess  of 
the  north  has  been  distinguished  as  belonging  to  separate  epochs, 
and  a  two-fold  division  of  the  same  in  the  south  has  been  men- 
tioned. The  yellow  loam  is  here  considered  as  the  interfluvial 
equivalent  of  the  loess,  but  there  seems  little  reason  for  making 
such  a  division." 

(23)  M.  S.  Fuller  and  E,  G.  Clapp  in  their  study  of  the  loess  of  the 
Wabash  river,  arrived  at  the  conclusion  that  the  marl-like  loess  is 
a  deposit  associated  with  the  glacial  waters  of  the  lowan  ice-sheet, 
and  is  not  different  in  age  from  the  northern  loess. 

Mr.  (24)  O'.  H.  Hershey  would  make  all  the  upland  loess  of  south- 
eastern Minnesota,  a  large  portion  of  central  and  southern  Illinois, 
southern  and  southeastern  Iowa,  northeastern  Kansas  and  eastern 
Nebraska,  with  a  possible  greater  extension  up  the  Ohio-Missouri 
rivers,  extensive  extra-glacial  lowan  silt.  In  so  doing,  Mr.  Hershey 
makes  his  upland  loess  and  his  lowland  loess  of  the  same  age. 

It  has  been  suggested  that  Mr.  (25)  Leverett,  in  his  Monograph  on 
the  Illinoian  Glacial  Lobe,  was  undecided  as  to  the  age  of  the 
loess.  After  having  questioned  the  existence  of  a  distinct  lowan 


/jo  THE  AGE  OF  THE  LOESS 

ice-sheet,  and  after  having-  made  a  study  of  the  drift  deposits  of 
Europe,  Mr.  Leverett  wrote  an  article  entitled  "Comparison  of 
North  American  and  European  Glacial  Deposits,"  in  which  he  refers 
to  a  loess  covering  the  earlier  Wisconsin  terminal  moraine  of 
central  and  eastern  Illinois.  He  notes  that  the  loess  is  about  a 
meter  in  thickness,  that  it  is  not  separated  from  the  Wisconsin 
drift  by  any  perceptible  weathering  or  erosional  interval,  and  that 
it  displays  all  the  appearance  of  having  been  deposited  as  the 
Wisconsin  ice  retreated. 

A  study  of  the  foregoing  evidence  seems  to  warrant  the  follow- 
ing conclusion  that,  in  most  cases,  the  loess  has  been  assigned  to 
different  epochs  upon  the  basis  of,  (i)  difference  in  color,  (2)  an 
apparent  difference  in  texture,  (3)  an  apparent  difference  in 
physical  aspect,  (4)  the  presence  of  a  distinct  ferruginous  band 
which  usually  separates  the  yellow  loess  from  the  gray  loess  and, 
(5)  the  stratigraphical  position  of  the  loess. 

Within  the  state  there  are  several  well  denned  geographical 
areas  where  the  loess  occurs.  These  areas  are,  (i)  around  the 
border  of  the  lowan,  (2)  along  the  margin  of  the  major  streams 
which  are  tributary  to  the  Mississippi  river  and  which  may  be 
found  immediately  south  of  the  border  of  the  lowan  drift,  (3)  along 
the  western  border  of  the  state  from  Sioux  City  to  Omaha,  (4)  on 
restricted  areas  within  the  lowan  border,  (5)  along  the  Mississippi 
river,  (6)  over  much  of  the  Kansan  and  Illinoian  drift-sheets. 

Along  the  lowan  border  the  loess  presents  several  marked  char- 
acteristics. It  is  found,  (i)  that  the  loess  has  here  pronounced 
thickness,  and  is  little  thicker,  if  any,  where  the  streams  cross  the 
lowan  margin  onto  the  Kansan  drift,  (2)  that  while  true  loess  is 
present  in  the  upper  part,  beneath  it,  it  becomes  ftore  or  less  sandy, 


Plate    X. 

Kansan    Loess    Topography    near    lowan    Border,    Oakdale,    Johnson 
county.      (Leighton) 

(3)  that  there  is  a  uniform  tendency  for  the  loess  to  thin  out  as 
the  distance  from  the  lowan  border  increases  and  to  become  less 
sandy,  more  clayey  and  less  porous.  Since  the  edge  of  the  lowan 
ice  expressed  itself  in  long,  narrow,  marginal-like  lobes,  the  thick- 
ened belt  of  loess  is  very  irregular,  reaching  much  farther  south  in 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  41 

some  places  than  in  others.  In  every  case  where  it  mantles  the 
Kansan  drift,  it  is  observed  to  rest  upon  an  eroded  surface  of 
hig-hly  oxidized  and  leached  drift,  or  on  Buchanan  gravel.  Fre- 
quently it  is  possible  to  find  the  loess  lapping  upon  the  lowan  drift 
some  distance  back  from  the  margin.  While  the  loess  reaches  its 
greatest  thickness  along  the  Missouri  and  Mississippi  rivers,  deposits 
of  considerable  depth  occur  along  the  Wapsipinicon,  Cedar,  Maquo- 
keta  and  Iowa  rivers,  especially  where  these  streams  pass  from  the 
lowan  area  to  the  Kansan.  It  is  quite  generally  agreed  that  the 
source  of  the  loess  is  from  the  glacial  drift,  having  been  separated 
from  it  by  the  work  of  the  rain,  wind,  plants,  birds,  insects  and  all 
forms  of  burrowing  life.  A  large  part  of  the  finely  comminuted 
material  would,  as  soon  as  dry,  be  picked  up  by  the  winds,  while 
still  other  portions  would  be  carried  by  the  run-off  to  the  major 
streams.  Streams  heavily  loaded  in  times  of  floods,  would  deposit 
much  of  the  fine  material  over  their  flood-plains  in  the  form  of 
bars  or  mud  flats.  When  the  water  receded,  and  the  sediment  be- 
came dry,  it  would  be  picked  up'  by  the  winds  and  deposited 
wherever  lodgment  was  afforded. 

The  agents  affecting  the  deposition  of  the  loess  are  vegetation 
and  topography.  It  is  well  known  that  forest  vegetation  is  earliest 
and  best  developed  along  streams.  This  being  true,  it  is  easy  to 
understand  why  the  loess  might  be  thicker  along  the  streams.  Not 
only  does  the  vegetation  act  as  a  barrier  to  the  winds,  but  the 
valley  walls  act  also  as  an  obstruction.  Strong  currents  of  air 
sweeping  up  from  the  valley  bottoms  and  impinging  on  the  steep 
bluffs,  produce  a  rarefaction  of  the  air  immediately  back  from  the 
bluff,  and  thus  a  deposition  of  the  wind's  load.  With  strong  pre- 
vailing westerly  winds  in  this  latitude,  and  favorable  conditions  for 
lodgment  of  the  loess,  there  should  be  a  thicker  mantling  of  the 
eastern  valley  slopes  than  the  western.  This  accounts,  possibly,  for 
the  pronounced  ridging  of  the  loess  so  common  near  the  above 
mentioned  streams. 

The  greatest  thickness  of  the  loess  is  found  along  the  eastern 
border  of  the  Missouri  river  valley,  where  it  reaches,  in  places,  a 
depth  of  50  to  100  feet.  There  are  differences  of  opinion  as  to  the 
age  of  the  loess  here.  There  are  those  who  would  make  it  the 
deposition,  largely,  of  one  interglacial  epoch,  while  there  are  still 
others  who  would  make  it  the  result  of  three  different  interglacial 
(26)  epochs.  When  studied,  however,  in  relation  to  the  drift  further  to 
the  east,  the  Missouri  river  loess  shows  a  very  striking  and  interest- 
ing stratigraphic  relation.  Along  the  Missouri  it  is  found  super- 
imposed upon  Kansan  drift,  but  when  traced  eastward  to  the 
margin  of  the  Wisconsin  terminal  moraine  border,  it  is  found  to 
disappear  suddenly  beneath  the  younger  drift.  In  no  instance  is  it 
found  to  mantle  the  Wisconsin  drift  for  any  great  distance  back 
from  the  Wisconsin  drift  border.  The  specific  instance  referred  to, 
is  in  the  vicinity  of  Carroll  (27)  county,  where  the  loess  is  found  to 
overlap  occasionally  for  short  distances,  the  Wisconsin  drift  border. 
This  overlapping  is  due  no  doubt  to  the  later  work  of  the  winds 
blowing  the  loess  from  the  Kansan  onto  the  Wisconsin  drift.  A 
careful  search  by  the  writer  for  other  places  where  loess  might  be 
found  on  the  Wisconsin  drift,  failed  to  reveal  any.  It  was  found 
that,  wherever  the  loess  occurs  over  the  Kansan  drift  between  the 
Missouri  river  and  the  margin  of  the  Wisconsin  drift,  it  is  fossil- 
iferous  whenever  it  reaches  a  depth  of  five  feet  or  more.  Where 
the  depth  is  less  than  five  feet  it  is  found  to  be  non-fossiliferous. 


42  DISTRIBUTION  OF  LOESS  WITHIN  THE  STATE 

This  fact  would  seem  to  indicate  quite  strongly,  that  the  loess 
deposit  is  of  more  recent  origin  than  immediately  post-Kansan. 
When  studied  with  regard  to  the  underlying  stratigraphic  relations, 
it  is  found  to  rest  quite  frequently,  upon  a  loess-like  clay 
much  like  the  loess-like  clay  found  mantling  the  Kansan  drift 
in  the  southern  part  of  the  state.  Dr.  (28)  George  F.  Kay, 
in  speaking  of  the  loess-like  clay  of  southern  Iowa  says  "while 
there  is,  in  places,  loess  of  eolian  origin  on  the  Kansan  drift 
of  southern  Iowa,  much  of  the  material  which  has  been  de- 
scribed as  loess  is  thought  to  be  not  of  eolian  origin,  but  to  be 
related  more  or  less  closely  to  the  Kansan  gumbo.  The  upper  few 
feet  of  the  Kansan  gumbo,  which  is  now  limited  to  the  tabular 
divides,  is  a  fine  grained,  loess-like,  joint  clay,  in  which  if  diligent 
search  is  made,  it  is  possible  to  find  a  very  few  very  small  pebbles 
similar  to  those  in  the  normal  gumbo,  and  it  is  thought  that  this 
loess-like  clay  is  the  result  of  changes  that  have  been  going  on  at 
and  near  the  surface  of  the  gumbo  during  the  great  length  of  time 
since  the  normal  gumbo  was  formed."  It  is  now  known  that  loess- 
like  clay  is  in  places  unconformable  writh  loess  where  loess  overlies 
it.  (29)  This  would  seem  to  establish  clearly  the  fact  that  the  loess  in 
this  southern  area,  is  not  immediately  post-Kansan.  If  the  loess 
here  were  of  Kansan  age,  it  would  seem  difficult  to  account  for  the 
fossiliferous  state.  Loess  exposed  at  the  surface  for  such  a  great 
length  of  time  as  would  be  involved,  wrere  it  Kansan  in  age,  would 
be  thoroughly  leached  and  oxidized,  thus  removing  all  traces  of 
shell  life. 

There  are,  within  the  lowan  drift  margin,  restricted  areas 
where  loess  forms  the  surface  covering  as,  for  example,  in  Bremer, 
Butler,  Black  Hawk,  Delaware,  Benton,  Clinton,  and  Mitchell  coun- 
ties. In  all  of  the  above  mentioned  areas  the  loess  is  found  to  lie 
upon  Kansan  drift,  or  upon  rock  hills.  The  former  relief  features 
are  called  pahas. 


Plate   XI. 

Loess    bordering    the    Kansan    Areas    southeast    of    Osage,    Mitchell 
county.      (Calvin) 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  43 

A  careful  study  of  these  areas  revealed  a  fossiliferous  loess  in 
almost  every  case,  where  the  loess  was  of  sufficient  depth.  Most  of 
the  places  examined  show  the  loess  to  be  thickest  on  the  lee  side. 
These  hills  are  to  be  interpreted  as  areas  where  the  pre-Kansan 
topography  was  so  rough  that  the  thin  lowan  ice  was  unable  to  pass 
over  them,  or  if  it  did  glaciate  them,  little  drift  was  left  on  them. 
During  the  loess  deposition  these  prominences  would  form  obstacles 
to  the  wind  currents  and  cause  deposition.  If,  as  suggested  by 
Alden  and  Leighton,  these  areas,  after  the  retreat  of  the  lowan  ice, 
were  the  first  to  become  clothed  with  vegetation,  a  further  obstacle 
to  dust  transportation  by  the  winds  would  be  offered.  Outside  the 
areas  above  described,  loess  has  been  reported  to  rest  on  lowan 
drift  in  the  vicinity  of  Denver  Junction,  Bremer  county. 


Plate   XII. 

lowan    drift    capped    by    loess-like    soil,    west    of    Denver    Junction, 
Bremer  county.      (Calvin) 


South  of  Latitude  410  50'  the  Kansan  drift,  except  in  regions 
bordering  the  Missouri  and  Mississippi  rivers,  is  mantled  with  a 
loess-like  clay  which  differs  from  true  loess  in  that  it  is  more  ashy 
in  color,  more  clay-like  in  character,  is  non-calcareous,  and  is  not 
sharply  set  off  from  the  underlying  drift  material.  As  has  already 
been  mentioned,  the  loess-like  clay  is  possibly  related  to  the  Kansan 
gumbotil  and  not  true  loess.  Doctor  (30)  Kay  holds  that  the  surface  of 
the  Kansan  drift,  after  the  Kansan  ice  withdrew,  was  a  ground 
moraine  plain,  which,  from  the  main  divide  between  the  Mississippi 
and  Missouri  rivers,  sloped  gently  southeast  to  the  Mississippi  river 


44 


RELATION  OF  THE  LOESS  TO  THE  DRIFT 


and  southwestward  to  the  Missouri  river.  This  drift  plain  was  so 
situated  topographically  that  the  weathering  agents  were  effective, 
but  erosion  slight.  As  a  result  of  the  weathering  during  an  exceed- 
ingly long  time  a  grayish,  tenacious,  thoroughly  leached  and  non- 
laminated  joint  clay  was  formed,  which  Doctor  Kay  has  called 
gumbotil. 


Figure  3. 

Undissected  Kansan   Gumbotil-Plain. 


After  a  long  period  of  quiescence  followed  by  diastrophism,  the 
streams  became  active  in  the  dissection  of  the  surface.  As  a  result 
of  a  long  erosional  period,  the  land  was  reduced  to  a  mature 
topography,  the  gumbotil  being  removed  everywhere  except  on  the 
interstream  divides  of  the  old  upland  plain. 


Figure   4. 

Dissected    Kansan    Gumbotil-plain. 


The  stratigraphic  relation  of  the  loess-like  clay  to  the  gumbotil 
is  of  importance  in  determining  its  age.  If  the  loess-like  clay  be 
the  result  of  the  further  weathering  of  the  gumbotil,  its  date  of 
origin  must  be  post  formation  of  the  gumbotil-plain. 


SOME   PHASES  OF  THE  PLEISTOCENE  OF  IOWA 


45 


Figure   5. 

Dissected  Kansan  Gumbotil-plain  showing  the  relation  of  the  loess- 
like  clay  to  the  gumbotil  and  Kansan  drift. 

From  figure  (5)  it  is  clearly  seen  that  the  loess-like  clay  has 
been  deposited  after  the  erosion  of  the  gumbotil-plain,  since  it 
mantles  not  only  the  gumbotil,  but  the  lower  spurs  from  which  the 
gumbotil  has  been  removed.  This  distribution  from  the  higher 
interstream  divides  has  been  affected  by  rain-wash,  wind  work, 
slumping,  and  other  transporting  agents.  This  clearly  makes  the 
loess-like  material  post-erosion  of  the  old  Kansan  gumbotil-plain  in 
age  and  not  loess  of  immediate  post-Kansan  age.  The  relation  of 
the  loess-like  clay  to  the  Kansan  drift  is  better  seen  by  a  study  of 
the  following  type  section  in  Lee  county  as  worked  out  by  A.  H. 
Dewey. 

Atchison,    Topeka    &    Santa    Fe    R.    R.    cut,    east    of    Nixon,    Iowa, 

Sec.  31,  T.  67,  R.  5  W. 
The  top  of  this  cut  is  at  the  level  of  the  Kansan  upland. 

Feet.  Inches. 

1.  Loess-like  clay.     The   top   two  feet  very  light   gray; 

below  yellow  to  light  brown  on  dry  surface; 
when  freshly  cut  into  a  chocolate  color  is  seen; 
the  whole  is  jointed  clay  and  grades  into  (2). 12 

2.  Typical  gumbotil   (Kansan).     Gray  on  a  dry  surface 

with  a  checked  appearance;  when  freshly  cut 
into  it  shows  a  drab  color;  very  sticky;  contains 
here  and  there  spots  of  brown.  Pebbles  are 
present;  the  whole  is  leached  and  grades  into 
(3)  , 12 

3.  Oxidized     and     leached     drift     (Kansan).      Contains 

pebbles  and  small  bowlders  and  lime  concre- 
tions. To  the  bottom  of  the  cut. 

Pebble  counts  from  the  above  section. 

Loess-like  clay '__6  pebbles  of  quartz  and  chert. 

Gumbotil    (Kansan) 100   pebbles. 

Quartz  51% Feldspar      3% 

Chert  34% Felsite          i% 

Greenstones    3% Sandstone  2% 

Granite  6% 

If  this  material  covering  the  gumbotil  is  loess  how  shall  the 
siliceous  pebbles  be  accounted  for?  In  a  study  by  several  workers 
of  many  sections  from  the  Kansan  drift  area,  in  the  southern  part 
of  the  state,  where  the  loess-like  clay  mantles  this  drift,  it  was 


46  RELATION  OF  THE  LOESS  TO  THE  DRIFT 

found  that  the  quartz  pebbles  were  present.  If  the  material  is 
related  to  the  gumbotil,  then  the  presence  of  the  quartz  pebbles 
may  be  explained. 

Mr.  (31)  F.  Leverett,  in  his  work  on  the  Illinoian  drift  in  Iowa, 
reports  the  entire  surface  covered  with  a  mantle  of  loess.  In 
writing  of  the  loess  he  says  "the  deposit  is  found  not  only  along 
the  streams,  but  on  the  divides  between  the  streams.  It  is  much 
thicker  along  the  borders  of  the  Mississippi  and  Illinois  rivers  than 
on  the  divides  between  them.  Over  much  of  the  southern  part  of 
the  Illinoian  drift  the  thickness  is  from  3  to  5  feet."  In  Iowa,  the 
reports  that  have  to  do  with  the  Illinoian  drift,  speak  of  it  as  being 
mantled  with  loess.  This  interpretation  is  correct.  However,  recent 
investigation  of  the  Illinoian  drift  in  Iowa,  shows  that  in  places  the 
Illinoian  gumbotil  is  covered  with  loess-like  clay  similar  to  loess- 
like  clay  covering  the  Kansan  in  southern  Iowa. 

If  the  main  body  of  the  loess  is  Peorian  in  age,  it  should  hold 
a  very  definite  stratigraphic  relation  to  the  Wisconsin,  the  youngest 
drift-sheet.  This  is  found  to  be  true.  From  the  edge  of  the 
lowan  border  the  loess  was  traced  westward  and  was  found  to  pass 
beneath  the  Wisconsin  drift.  The  eastern  edge  of  the  Wisconsin 
drift  was  traced  from  Eldora,  Hardin  county,  south  to  the  southern 
edge  of  the  Wisconsin,  in  Marshall  county,  and  data  from  sections 
and  wells  were  obtained.  Many  sections  might  be  given  where  loess 
was  found  to  be  present  beneath  the  Wisconsin.  One  of  the  best 
localities  to  show  the  stratigraphic  relations  of  the  loess  to  the 
Wisconsin  and  underlying  drift  is  found  in  the  vicinity  of  Rhodes, 
in  the  southwest  part  of  Marshall  county. 


Plate  XIII. 


Cut  showing  the  relation  of  the  loess  to  the  Wisconsin  and  Kansan 

drifts.      (Alden) 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  47 

It  will  be  seen  that  the  loess  here  rests  upon  Kansan  gumbotil 
and  is  overlain  by  Wisconsin  drift.  Many  other  sections  might  be 
given,  all  showing  this  same  stratigraphic  relation  of  the  loess  with 
respect  to  the  Wisconsin,  when  traced  westward  from  the  lowan 
border.  A  study  of  the  loess  on  the  western  margin  of  the  Wis- 
consin drift  reveals  the  same  stratigraphic  relations  as  are  found 
on  the  eastern  Wisconsin  margin. 

The  age  of  the  loess  may  be  determined  by,  (i)  its  strati- 
graphic  position  with  relation  to  other  drift-sheets,  (2)  unconform- 
ities in  the  loess  body  itself  and,  (3)  the  physical  and  chemical 
changes  which  the  loess  has  undergone.  If  the  loess  had  its  origin 
in  fresh  unweathered  glacial  drift,  it  should  show  many  of  the 
same  elements  contained  in  the  drift.  An  analysis  of  the  loess 
shows  it  to  be  composed  largely  of  silica,  feldspar,  hornblende, 
pyroxene  and  mica.  These  are  the  dominant  minerals  found  in  the 
glacial  drift  which  is  strong  evidence  that  the  loess  must  have 
come  from  the  igneous  and  sedimentary  rocks  which,  decomposable 
on  prolonged  weathering,  would  yield  the  minerals  of  the  loess. 

The  high  percentage  of  magnesium  and  calcium  carbonates 
independent  of  the  presence  of  shell  life,  indicates  that  the  loess 
coujd  never  have  been  derived  from  the  residual  clays. 

If  the  loess  was  originally  calcareous,  it  must  have  been  derived 
from  a  drift  that  was  fresh  and  unleached,  and  accumulated  suffi- 
ciently rapid  that  leaching  and  oxidation  could  not  keep  pace  with 
the  rate  of  accumulation.  Unconformities,  such  as  erosional  sur- 
faces and  soil  bands  within  the  body  of  the  loess,  would  be  positive 
evidence  of  more  than  one  loess  making  epoch.  Since  no  such 
evidence  has  been  obtained,  the  division  of  the  loess  has  been  made 
upon,  (i)  the  difference  in  color,  (2)  the  presence  of  a  ferruginous 
band  located  generally  between  the  yellow  and  gray  loess  and,  (3) 
textural  differences.  Earlier  investigators  of  loess  gave  little  atten- 
tion to  the  problem  of  leaching  and  oxidation,  but  it  now  seems 
that  this  factor  has  become  one  of  the  most  important  factors  in 
determining  the  age  of  loess.  As  has  been  shown  already,  leaching 
and  oxidation  of  the  loess  are  the  result  largely  of  the  action  of 
meteoric  waters.  The  factors  affecting  the  depth  of  leaching  and 
oxidation  of  the  loess  are,  (i)  the  porosity  of  loess,  (2)  the  height 
of  ground  water,  which  in  turn  is  affected  by  several  factors  and, 
(3)  the  chemical  composition  of  the  loess. 

In  making  a  study  of  the  depth  of  leaching  and  oxidation  all 
of  the  above  mentioned  factors  need  to  be  taken  into  consideration. 
In  many  of  the  areas  studied,  where  the  loess  was  of  sufficient 
depth,  two  colors  were  universally  seen;  the  gray  loess  below  and 
the  yellow  loess  above.  Because  of  the  presence  of  these  two  colors 
there  are  those  who  would  make  the  gray  loess  immediately  post- 
Kansan  in  age,  and  the  yellow  loess,  immediately  post-Iowan.  A 
careful  investigation  has  been  made  of  many  exposures  where  the 
two  colors  may  be  seen  with  the  result  that  color  cannot  be  used 
to  separate  loess  into  different  ages.  There  is  no  zone  of  leaching 
or  any  other  weathering  effects  in  the  top  of  the  gray  loess.  The 
following  is  a  type  section  which  shows  the  average  relations  of  the 
gray  loess  to  the  yellow  loess. 


OXIDATION  AND  LEACHING  OF  THE  LOESS 


Plate  XIV. 


Section  in  Brick  Yard  east   of  Lucas   and   north   of  Ronald   streets, 
Iowa   City,    Johnson   county. 

Feet.  Inches. 

i.  Loess  yellow,  streaked  with  iron  stains;  upper  2  feet 
leached  and  non-fossiliferous;  the  lower  part 
highly  fossiliferous 5 


2.  Ferruginous     band      containing      fossils      and      iron 

tubules  passing  from  zone   (i)   into  zone  (3) 

3.  Loess  gray,  unleached  and  highly  fossiliferous 2 


2-4 


In  this  specific  case  iron  tubules,  shown  by  the  vertical  lines  on 
the  above  plate,  were  found  to  pass  from  the  portion  of  the  yellow 
loess  through  the  ferruginous  zone  into  the  gray  loess  below. 
Shells  were  found  also  to  pass  from  the  lower  portion  of  the  yellow 
zone  through  the  ferruginous  band  into  the  gray  loess  below. 

The  fossils  from  these  three  zones  were  compared  with  the 
fossils  taken  from  these  same  three  zones  from  loess  obtained  at 
Des  Moines.  The  following  plate  shows  the  results  obtained. 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  tO'WA 


49 


Plate  XV. 

Fossils  of  the  loess. 

The  upper  row  consists  of  shells  taken  from  the  yellow  loess  at 
Iowa  City  and  Des  Moines;  the  middle  row  shows  shells  obtained 
from  the  ferruginous  band  from  the  same  localities  as  mentioned 
above;  the  lower  row  shows  shells  secured  from  the  gray  loess  at 
Iowa  City  and  at  Des  Moines.  The  only  difference  noted  is  a  slight 
difference  in  size,  but  this  variation  may  be  found  in  any  one  of 
the  above  mentioned  horizons. 


THE  LOESS  FOSSILS  AND  THEIR  VALUE 


Plate  XVI. 

Loess  section   showing  zone  of  loess-kindchen  and  iron  connections. 

In  the  lower  part  of  the  yellow  loess  and  the  upper  of  the  gray 
there  may  be  seen  iron  pipe  stems  and  loess  kindchen.  An  exam- 
ination of  the  above  plate,  taken  in  the  west  end  of  a  cut  in  an 
Iowa  City  brick  yard,  shows  the  loess  filled  with  loess  kindchen,  the 
white  irregular  pebbles  shown  in  horizon  (2).  In  studying  the 
problem  of  leaching  and  oxidation  of  loess,  where  it  was  found 
associated  with  the  Wisconsin  border,  the  cuts  west  of  Rhodes  and 
in  the  vicinity  of  Carroll  are  taken  as  types. 

Rhodes  Cut  located  on  the  C.  &  Milwaukee  R.  R.  two  miles  west  of 

Rhodes.  Feet.  Inches. 

1.  Soil   ashy  gray 10 

2.  Drift  yellow,    the   upper   two   feet   leached;    contains 

numerous  limestone  pebbles  (Wisconsin) 22 

3.  Loess    yellowish,    calcareous    and    fossiliferous;     the 

whole     streaked     with     gray;     in     places     large 
pockets  of  gray  loess  may  be  seen 31 

4.  Ferruginous    zone    of    varying    width    and    sinuous, 

also     fossiliferous 2  4 

5.  Loess    gray,    unleached    and    fossiliferous    resting   on 

Kansan    gumbotil 24 

6.  Kansan    gumbotil,    grayish    and    streaked   with    spots 

of   brown 12 

7.  Leached   Kansan   drift Base. 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA         5i 


Plate  XVII. 

Cut  two  miles  west  of  the   town  of  Rhodes,   Marshall  county. 

Here  the  loess  is  calcareous  throughout.  It  is  sharply  set  off 
from  the  Kansan  gumbotil  and  the  line  between  the  Wisconsin 
drift  and  the  loess  above  is  sharply  drawn.  This  may  be  seen  from 
an  examination  of  the  above  plate.  The  upper  six  feet  of  the 
yellow  loess  contains  the  loess  kindchen. 

Cut  north  of  Carroll  on  C.  &  G.  W.  R.  R. 

Feet.  Inches. 

1.  Soil,   grayish   black 10 

2.  Wisconsin    drift,    grayish    to    yellowish    buff,    upper 

four  feet  leached  and  oxidized 6 

3.  Loess,    yellowish    gray    to    buff,    the    upper    two    feet 

leached,   the  lower  unleached  and   fossiliferous; 
patches  of  gray  present 10 

4.  Oxidized  layer  of  loess  with  iron 2-3 

5.  Loess,  bluish  gray  and  fossiliferous 6 

6.  Soil  band  containing  carbonaceous  matter i 

7.  Kansan     gumbotil 18 

The  two  loesses  reported  from  Winneshiek  county  by  Professor 
Calvin  show  similar  conditions. 


OXIDATION  AND  LEACHING  OF  THE  LOESS 


Plate  XVIII. 

Loess  cut,  Sec.  3,  Decorah  township,  Winneshiek  county.     (Shimek) 

The  dark  line  in  the  plate  is  the  ferruginous  band  separating 
the  two  colors.  This  was  the  dividing"  line  between  the  Kansan 
loess  below  and  the  lowan  loess  above.  Many  other  sections  might 
be  given  showing  the  same  relations  as  already  indicated.  The 
foregoing  evidence  would  seem  to  warrant  the  conclusion  that  the 
loess  must  have  come  from  a  drift  that  was  highly  calcareous,  and 
must  have  been  deposited  so  fast  that  oxidation  and  leaching  had 
little  effect  during  the  time  of  accumulation.  The  loess  was  origin- 
ally gray  in  color,  and  the  two  colors  now  seen  so  commonly  are 
the  result  of  the  oxidation  of  the  upper  portion  of  the  loess  since 
its  deposition.  The  iron  band  so  persistent  beween  the  yellow  and 
the  gray  loess  represents  the  zone  of  redeposition  of  the  iron 
material  leached  out  from  the  overlying  loess.  The  iron  concre- 
tions and  loess  kindchen  represent  also  material  leached  from  the 
loess  and  redeposited. 

As  to  textural  differences,  there  is  great  variation  from  place 
to  place  and  even  in  the  same  deposit  at  any  one  place.  Some  areas 
will  show  loess  that  is  very  sandy,  while  others  will  show  a  more 
clayey  composition.  A  study  was  made  of  the  loess  from  the  yellow 
zone,  the  ferruginous  zone  and  the  gray  loess  from  numerous  cuts. 
Slides  were  made  and  examined  under  the  microscope  to  see  if  the 
difference  in  the  shapes  of  the  particles  and  percentage  of  different 
minerals  varied  from  the  yellow  to  the  gray  in  any  one  section, 
where  both  were  present,  with  the  result  that  there  was  practically 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  53 

no  difference  in  either  shape  of  particles  or  percent  of  mineral 
content  in  any  of  the  three  zones,  the  yellow  band,  the  ferruginous 
band  or  the  gray  band. 

As  previously  mentioned  (see  Plate  XV.),  the  fossil  life  of  the 
loess  is  of  little  value  in  determining  the  age  of  the  loess,  since 
there  is  little  change  in  species  of  the  Molluscan  life. 


Plate  XIX. 

Fossil  Life  of  the  Loess. 

The  upper  row  represents  shells  obtained  from  loess  near  the 
border  of  the  lowan  in  Marshall  county.  The  middle  row  are  shells 
from  the  ferruginous  zone  at  Rhodes,  while  the  lower  are  shells 
collected  from  the  gray  loess  at  Rhodes.  If  there  is  any  value  in 
the  shell  life  at  all  in  helping  to  determine  the  age  of  the  loess,  it 
might  be  said  that  there  is  no  difference  in  age  between  the  gray 
and  the  yellow  loess.  The  greatest  difference  noted  in  the  study  of 
the  shell  life,  was  the  variation  in  size,  which  according  to 
Professor  Shimek,  is  due  to  surface  conditions  during  the  time  of 
habitation  and  not  to  difference  in  time. 

The  study  of  the  loess  has  led  to  the  following  conclusions: — 
;(i)  the  source  of  the  loess  was  chiefly  the  fresh,  unweathered  gla- 
I  cial  drift,  some  of  which  may  have  come  from  the  silts  of  glacio- 
'  fluvial  waters  and  silts  from  dried-up  lakes  and  river-flats;  (2)  the 
difference  in  texture  does  not  mean  necessarily  a  difference  in  the 
age  of  deposition  of  the  loess,  but  is  what  might  be  expected  if 
winds  are  the  distributing  agent;  (3)  the  mass  of  the  loess  was 
originally  gray  in  color,  the  differences  in  the  color  seen  now  are 
the  result  of  oxidation  and  leaching.  Where  the  loess  is  thick 
enough,  so  that  oxidation  and  leaching  have  not  reached  to  the 
base,  the  yellow  loess  is  found  above  and  gray  loess  below.  The 
presence  of  grayish  streaks  and  patches  throughout  the  yellow 
lends  weight  to  this  conception;  (4)  the  ferruginous  zone,  which  has 
been  thought  to  represent  the  old  erosional  surface  of  the  gray 
loess  is  but  the  horizon  where  meteoric  waters,  highly  charged  with 


54  CONCLUSIONS  AS  TO'  THE  AGE  OF  THE  LOESS 

the  iron  content  leached  from  the  overlying  loess,  have  become 
saturated  and  have  redeposited  their  load.  That  this  is  true  is 
further  strengthened  by  the  presence  of  fossil  life  in  the  zone  and 
the  iron  pipestems  which  have  been  found  to  pass  from  the  yellow 
zone  into  the  gray  loess  beneath;  (5)  some  of  the  loess-like  ma- 
terial, found  mantling  the  drift  in  the  southern  part  of  the  state, 
may  not  be  loess  but  be  related  to  the  Kansan  gumbotil;  (6)  the 
overlapping  of  the  lowan  drift  border,  and  the  mantling  of  local 
areas  within  the  lowan  margin,  do  not  prove  the  loesses  to  be  of 
different  ages.  Withdrawal  of  the  lowan  ice  edge,  if  loess  deposi- 
tion was  in  progress,  would  offer  conditions  favorable  to  lodgment 
where  vegetation  may  have  gotten  started  on  the  newly  glaciated 
surface;  (7)  the  study  of  the  fossil  life  while  of  little  value  in  de- 
termining the  mode  of  genesis  and  age  of  the  loess,  is  of  great 
value  in  working  out  the  manner  of  its  distribution  and  certain 
climatic  conditions  during  its  deposition;  (8)  physical  analyses  of 
the  gray  and  yellow  loesses  of  many  sections,  fail  to  show  any 
great  differences  in  the  shapes  and  sizes  of  the  particles,  or  any 
great  variation  in  the  kind  and  number  of  minerals  present;  (9) 
that  while  several  loesses  have  been  reported,  there  seems  to  have 
been  one  epoch  more  favorable  for  loess  accumulation  than  any 
other.  This  epoch  followed  the  retreat  of  the  lowan  ice  and  is 
known  as  the  Peorian  interglacial  epoch.  During  the  Peorian 
epoch  the  rate  of  accumulation  of  loess  must  have  exceeded  the 
rate  of  leaching  of  the  lime  carbonate.  The  epoch  may  be  said  to 
have  come  to  a  close  when  the  rate  of  leaching  and  oxidation  ex- 
ceeded the  rate  of  accumulation. 


BIBLIOGRAPHY. 

1.  D.   D.   Owen.     The   loess   of   the   Des   Moines   and    the    Missouri 

rivers.  Senate  Document  26th  Congress,  second  series,  Vol. 
5,  Pt.  II.  237,  Washington  1871. 

2.  W.  H.  Pratt.     Loess  near  Davenport.       Proc.  Davenport  Acad. 

Sciences,  Vol.  i,  1867-1868,  p.  56. 

3.  C.  A.  White.     The  bluff  deposit.     la.  Geol.  Survey  Reports,  Vol. 

i,  1870,  pp.  103-109.  Proc.  Amer.  Association  for  the  Ad- 
vancement of  Science,  Vol.  27,  1878,  p.  231. 

4.  J.   E.   Todd.      Relation   of   the   loess   to   drift    in   southern   Iowa. 

Proc.   la.  Acad.  Sciences,   1875-1880. 

More  light  on  the  origin  of  the  Missouri  river  loess.     Amer. 

Jour.  Science,  Vol.   16,   1906,  pp.   181-194. 

5.  R.    E.    Call    and    W    J    McGee.      On    the    loess    and    associated 

deposits  of  Des  Moines.  Proc.  Amer.  Association  for  the 
Advancement  of  Science,  Vol.  27,  pp.  21-22.  The  loess  in 
central  Iowa.  American  Naturalist,  Vol.  15,  1881,  p.  72. 

6.  F.    N.    Witter.      Loess   of  Muscatine.     Proc.    la.   Acad.    Sciences, 

1875-1880,  p.   16. 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  55 

7.  W    J    McGee.      The    Pleistocene    history    of    northeastern    Iowa. 

Eleventh  Annual  Report  U.  S.  Geological  Survey,  Vol.  n, 
1890,  pp.  291-303.  Philosophical  Society  of  Washington, 
Nov.  10,  1883. 

8.  T.  C.  Chamberlin  and  R.  S.  Salisbury.     The  loess  of  the  "Drift- 

less  Area."  Sixth  Annual  Report  U.  S.  Geological  Survey, 
1884-1885,  pp.  278-306. 

9.  B.  Shimek.     The  loess.     Bull.  Natural  History  State  University 

of  Iowa,  Vol.  5,  1904,  pp.  341,  359,  360.  A  theory  of  loess. 
Proc.  la.  Acad.  Sciences,  Vol.  3,  1895,  p.  82.  The  genesis  of 
the  loess,  a  problem  in  plant  ecology.  Proc.  la.  Acad. 
Sciences,  Vol.  15,  1908,  p.  57.  The  loess  of  the  Missouri 
river.  Proc.  la.  Acad.  Sciences,  Vol.  14,  1907,  p.  237.  The 
distribution  of  loess  fossils.  Jour,  of  Geology,  Vol.  7,  1899, 
p.  122. 

10.  B.  Shimek.  Geology  of  Harrison  and  Monona  counties.  la. 
Geol.  Surv.  Reports,  Vol.  20,  1909,  pp.  376-404.  Loess  and 
the  Lansing  man.  Bull.  Lab.  Natural  History  State  Univer- 
sity of  Iowa,  Vol.  5,  1904,  pp.  337-340. 

IT.  S.  Calvin.  Geology  of  Johnson  county.  la.  Geol.  Surv.  Reports, 
Vol.  7,  1896,  pp.  88-90. 

12.  S.  Calvin.     Geology  of  Howard  county.     la.  Geol.  Surv.  Reports, 

Vol.   13,   1902,  p.  70. 

13.  S.    Calvin.      Present    phase    of    Pleistocene    problems    in    Iowa. 

Bull.   Geol.   Soc.  America,  Vol.   20,    1910,   pp.    133-152. 

14.  H.    W.    Norton.      Geology    of    Bremer    county.      la.    Geol.    Surv. 

Reports,  Vol.  16,  1905,  p.  376. 

15.  J.    L.    Tilton.      Geology    of    Warren    county.      la.    Geol.    Surv. 

Reports,  Vol.  5,   1895,  p.  318. 

16.  R.  S.  Salisbury.     Loess  in  Wisconsin  drift   formation.     Jour,  of 

Geology,  Vol.  4,   1898,  p.  929. 

17.  R.    S.     Salisbury.       Geology    of    Crowley's    Ridge.       Ark.    Geol. 

Survey,  Vol.   2,    1889,   pp.   230-231. 

18.  J.  A.  Udden.     Silveria  formation  and  other  silt  deposits.     Mono- 

graph U.  S.   Geol.  Survey,  Vol.  38,   1899,   pp.    114-115. 

19.  O.   W.   Wilcox.     On   certain   aspects   of   the   loess   of   southwest 

Iowa.     Jour,  of  Geol.  Vol.   12,   1904,  p.  716. 

20.  W.   H.    Pratt.      Loess   near   Davenport.      Proc.    Davenport   Acad. 

Sciences,   Vol.    i,    1876,   pp.   96-99. 

21.  H.  F.  Bain.     Geology  of  Carroll  county.     la.  Geol.  Surv.  Reports, 

Vol.   9,    1898,   p.   91. 

22.  T.  O.  Mabry.     The  brown  or  yellow  loam  of  north  Mississippi, 

and  its  relation  to  the  northern  drift.  Jour,  of  Geology, 
Vol.  6,  1898,  p.  273. 


56  BIBLIOGRAPHY 

23.  1VL  S.    Fuller   and   E,    G.    Clapp.      The   marl-loess    of    the   lower 

Wabash  valley.     Jour,  of  Geology,  Vol.  n,  1903,  p.  116. 

24.  O.   H.  Hershey.      Derivation   of   the  loess   of   the   common   type. 

Bull.  Geol.  Soc.  America,  Vol.  14,  1903,  p.  169. 

25.  F.    Leverett.      The    lowan    drift-sheet    and    associated    deposits. 

Monograph  U.  S.  Geological  Survey,  Vol.  38,  1898,  pp.  131, 
*37>  T38,  143,  153.  Comparisons  of  North  American  and 
European  glacial  drifts,  1910,  p.  299. 

26.  B.    Shimek.      Geology    of    Harrison    and    Monoria    counties,      la. 

Geol.  Surv.  Reports,  Vol.   20,    1909,  pp.   376,   378,   386. 

27.  H.   F.   Bain.     Geology   of   Carroll   county.      la.    Geol.    Surv.    Re- 

ports, Vol.  9,   1898,  p.  91. 

28     G.    F.    Kay.      Gumbotil,    a    new    term,    in    Pleistocene    geology. 
Science  new  series,  Vol.  44,   1916,  p.  637. 

29.  G.   F.   Kay.     Personal   communication. 

30.  G.    F.    Kay.      Some    features   of    the    Kansan    drift    of    southern 

Iowa.     Bull.  Geol.  Soc.  America,  Vol.  27,   1918,  p.   115. 

31.  F.    Leverett.      The    Illinoian    glacial    lobe.      General    aspects    of 

Illinoian  drift-sheet.  Monograph  U.  S.  Geological  Survey, 
Vol.  38,  1899,  pp.  32,  42,  183,  184.  Comparison  of  North 
American  and  European  glacial  deposits,  1910,  p.  299. 

32.  S.    Calvin.      Geology    of   Winneshiek    county.      la.    Geol.    Surv. 

Reports,  Vol.  16,  1905,  pp.  126-127. 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  57 

CHAPTER  V. 

THE   PEORIAN   INTERGLACIAL   EPOCH. 

The  evidence  of  a  Peorian  interglacial  epoch  was  based  first 
upon  the  presence  of  fossiliferous  loess  beneath  the  drift  of  the 
Shelbyville  lobe  of  the  early  Wisconsin  and  superimposed  upon  a 
peat  and  muck  horizon  of  known  Sangamon  age. 


Plate  XX. 

Cut    east   of   Peoria,    Illinois,    showing    fossiliferous   loess    resting   on 
Sangamon  soil.      (Leverett) 

As  stated  previously,  Mr.  Leverett  has  reported  rather  extensive 
deposits  of  peat  and  muck  at  the  base  of  the  Wisconsin  drift  in 
McHenry,  Karte,  DeKalb  and  LaSalle  counties,  Illinois. 

More  recent  work  on  the  drifts  in  Illinois  would  seem  to  make 
it  very  doubtful  whether  Towan  drift  underlies  the  Wisconsin  in 
the  above  areas  cited  by  Leverett.  Since  the  above  evidence  was 
obtained  from  well  data,  it  should  not  be  taken  as  proving  that  the 
soil  horizon  here  referred  to  is  of  Peorian  age.  It  is  just  as  likely 
to  be  Sangamon  or  Yarmouth  in  age  as  Peorian.  The  Toronto  beds 
have  been  assigned  by  T.  C.  Chamberlin  to  the  (!)  Peorian.  Professor 
Chamberlin  remarked  when  he  introduced  the  term  "that  the 
grounds  for  correlating  these  deposits  with  the  Peorian  interglacial 
deposits  of  Illinois,  are  not  strong  and  that  further  investigation 
may  show  these  gounds  to  be  erroneous."  He  further  states  "that 
whether  the  Don  beds  belong  to  the  Peorian  or  not,  it  is  certain 


58  THE  TORONTO  BEDS 

that  vegetal  beds  were  formed  in  the  interval  of  retreat  between 
the  formation  of  the  lowan  till  and  the  Wisconsin  till,  and  that 
some  of  these  less  well  developed  and  less  well  known  deposits  must 
be  looked  to  as  a  type  of  this  interglacial  horizon  if  the  Toronto 
beds  prove  unreliable.  Mr.  Leverett  in  speaking  of  the  Toronto 
beds  questioned  seriously  whether  they  should  be  assigned  to  this 
horizon,  as  it  is  his  opinion  that  there  is  no  lowan  drift  represented 
here.  The  drift  underlying  these  beds  is  held  by  Mr.  Leverett  to 
be  Illinoian  and  not  lowan.  If  this  is  true,  the  deposits  represented 
by  the  Toronto  beds  must  include  the  time  allotted  to  both  the 
Sangamon  and  Peorian  interglacial  epochs.  It  would  be  very 
difficult  to  determine  the  exact  time  of  deposition  of  these  beds, 
since  they  do  not  hold  a  definite  stratigraphic  position  where  the 
Wisconsin  drift  overlaps  the  lowan,  which  would  be  the  ideal  con- 
dition. 

To  better   understand   the   relation   of   the   Toronto   beds   to    the 
drift-sheets,   the   following  theoretical  diagram   is   here  given. 


Figure    6. 

Theoretical   diagram    of   the   Toronto   beds. 

5.     Sand,    stratified    and   containing   trees    like    those    in 
number     (4) 


Feet. 


55 


4.     Peaty  clays   containing   trees   and   other  plants   of  a 

cool    temperate   climate 94 

3.  Stratified  clays  and  sands  containing  leaves  and 
trunks  of  trees  as  well  as  unio  shells,  which 
are  now  found  in  middle  latitudes  of  the 
United  States 41 

2.  Old  bowlder  clay;  deposits  resting  on  preglacial 
surface  of  the  Hudson  river  shale  (probably 
Illinoian)  ? 

i.     Hudson   river  shale Base. 

Beds  marked  (3)  in  the  above  diagram  are  the  Don  beds,  and 
those  marked  (4)  and  (5)  are  called  the  Scarboro  beds.  After  the 
deposition  of  the  Illinoian  till  (2)  of  the  above  figure,  a  long  period 
of  erosion  ensued  during  which  time  a  deep  valley  was  cut  into  the 
drift,  and  sixteen  feet  into  the  underlying  Hudson  river  shale. 
Upon  this  old  surface  there  developed  a  vegetation  in  which  grew 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  59 

forest  trees,  which,  according  to  Professor  Penhallow,  were  much 
like  those  found  in  southern  latitudes,  in  the  vicinity  of  Pennsyl- 
vania. 

In  this  old  valley  was  deposited  coarse  shingle  with  which  was 
mixed  trunks  and  branches  of  red-cedar,  elm,  oak  and  pawpaws. 
Later,  owing  to  rise  of  water  in  Lake  Ontario,  which  was  possibly 
due  to  the  damming  of  the  lake's  eastern  outlet  by  ice,  a  deposit  of 
sand  and  gravel  to  the  depth  of  sixty  feet  was  made  in  the  lower 
part  of  the  valley.  It  is  in  these  beds  that  A.  P.  Coleman  found 
leaves,  woods,  and  unio  shells.  An  examination  of  the  fossil 
remains  by  Professor  Penhallow  leads  him  to  conclude  that  the 
time  represented  by  the  Don  deposits  was  one  of  moderate  climate 
for  this  northern  region.  After  the  formation  of  the  Don  beds,  a 
further  deeping  took  place,  until  the  water  level  stood  150  feet 
higher  than  at  the  present  time.  Into  the  lake  at  this  point  flowed 
a  large  river,  which,  according  to  Professor  Coleman,  was  the  outlet 
of  the  upper  lake-region  of  interglacial  time.  The  rise  of  the  lake 
water  produced  a  wide,  deep  bay  into  which  the  river  deposited  its 
clay  and  sand  in  the  form  of  a  large  delta.  That  the  deposit  was 
in  the  form  of  a  delta  is  shown  by  the  fine  lamination  and  stratifi- 
cation lines  throughout  the  deposit.  In  these  clays  (4)  of  figure  (6) 
peaty  material  was  obtained.  In  the  sands  and  gravels  near  the 
top  (5)  of  figure  (6)  were  found  fossil  unio  shells  and  beetle  wings. 
A  study  of  this  fauna  and  flora  by  Professor  Scudder,  revealed  a 
climate  much  cooler  than  is  indicated  by  the  fauna  and  flora  of  the 
Don  beds,  and  one  which  was  more  like  the  present  climate  of  the 
Ontario  region  of  to-day.  It  was  because  of  this  interpretation 
placed  upon  the  fossil  life  that  Professor  Coleman  has  interpreted 
these  beds  as  representing  the  outwash  of  the  advancing  Wisconsin 
ice-sheet. 

During  the  last  two  years  a  study  of  the  insect  life  of  the 
Sangamon  beds  has  been  made  by  Professor  Wickham  of  Iowa  State 
University.  The  Mahomet  beds  are  located  near  Mahomet,  Illinois, 
and  belong  to  the  Sangamon  interglacial  epoch.  By  a  study  of  the 
incect  life  of  this  horizon  it  becomes  possible  to  make  a  comparison 
of  two  widely  separated  American  faunas  which  are  thought  to 
belong  to  the  same  interglacial  stage,  the  Sangamon.  Professor 
Scudder  recognized  in  the  Scarboro  beds  76  species  of  33  genera  and 
8  families,  and  reached  the  conclusion  that  the  climate  of  Ontario, 
at  the  time  of  the  deposition  of  the  beds,  was  similar  to  that  found 
in  the  same  region  to-day,  or  perhaps  slightly  cooler,  since  a  num- 
ber of  the  recent  allies  of  the  fossils  have  now  a  more  northern 
habitat.  Professor  Wickham,  in  his  study  of  the  Mahomet  collec- 
tion, found  10  determinable  species  belonging  to  seven  genera  and 
four  families,  these  families  containing  as  well  the  bulk  of 
Scudder' s  Scarboro  species  in  the  proportion  of  36,  8,  19  and  12, 
respectively;  that  is,  65  species  out  of  the  76  which  Scudder  de- 
scribes, and  five  of  the  genera,  are  common  to  both  of  the  collec- 
tions but  all  the  species  appear  to  be  quite  different.  Professor 
Wickham  contends  that  the  basis  for  deductions  as  to  climate  is 
not  very  broad,  but  is  of  the  opinion  that  the  presence  of  Carabus 
meander  sangamon  and  Chlaenius  plicatipennis,  the  general  north- 
ern flavor  of  the  remaining  species  and  the  entire  absence  of  any 
without  fairly  close  recent  boreal  allies,  suggests  a  more  rigorous 
climate  than  that  found  in  southern  Illinois  at  the  present  time. 
Possibfy  the  climatic  conditions  were  as  severe  here  as  they  were  in 
Ontario  at  the  date  of  the  formation  of  the  Scarboro  beds.  It  is 


60  LIFE  OF  MAHOMET  AND  SCARBORO  BEDS 

known  that  the  same  genera  are  living  in  Illinois  to-day,  but  they 
occur  also  very  far  to  the  north,  extending  in  part,  to  the  very 
shores  of  the  Arctic  ocean.  It  would  thus  seem  that  an  account 
must  be  taken  of  the  entire  absence  of  anything  characteristically 
southern.  While  the  species  described  by  Professor  Scudder  are  all 
different  from  those  described  by  Professor  Wickham,  they  are 
very  closely  allied.  The  differences  are  not  great  enough  to 
indicate  any  wide  dissimilarity  in  ecological  conditions  nor  a  sep- 
aration by  a  long  period  of  time,  neither  do  the  likenesses  prove 
that  the  beds  in  question  were  synchronous.  If  the  Sangamon  was 
20,000  to  100,000  years  in  length,  and  granting  both  beds  in  question 
were  deposited  during  the  same  stage,  their  formation  still  might 
be  separated  by  thousands  of  years,  certainly  long  enough  to  bring 
about  a  differentiation  in  species.  In  making  comparisons  of 
species,  when  attempting  to  correlate  widely  separated  geological 
deposits  widely  different  lithologically  and  stratigraphically,  we 
must  consider  also  the  wide  separation  in  space  of  the  two  places 
in  question.  Professor  Wickham  questions  whether  10  species  of 
the  Carabiddae,  Dytiseidae,  Staphylinidae  and  Chrysomelidae,  taken 
at  random  in  a  recent  Illinois  bog,  would  all  be  different  from  65 
species  of  the  same  families  collected  during  the  same  year  and  in 
similar  surroundings  at  Toronto.  Seasons  may  have  little  to  do 
with  the  divergence  of  the  character  of  the  fossils,  since  the  peat 
deposits  in  which  the  fossils  are  found,  are  forming  throughout  the 
warmer  part  of  the  year  as  well  as  the  colder,  so  that  insect 
remains  might  readily  be  preserved  at  any  time.  The  fact  that 
there  is  no  evidence  of  intrusion  of  more  southern  types  in  the 
Mahomet  beds  would  suggest  that  the  deposits  perhaps  formed 
when  the  Illinoian  glacial  lobe  was  well  advanced  on  its  southern 
route,  previous  to  a  far  northern  recession.  The  conclusion  reach- 
ed, so  far  as  the  study  of  the  Mahomet  species  is  concerned,  is  that 
there  is  no  definite  way  of  determining  whether  the  Mahomet  fauna 
is  more  closely  related  to  the  Scarboro  fauna  or  to  those  of  the 
present  day.  All  three,  Professor  Wickham  thinks,  would  be 
similar  to  a  general  facies. 

The  conclusions  reached  from  a  comparative  study  of  the 
faunas  of  two  widely  separated  interglacial  deposits,  is  that  it  is 
not  possible  to  determine  positively  the  exact  time  relations  of  the 
Scarboro  beds,  but  indications  point  to  a  nearer  relationship  with 
the  Sangamon  interglacial  epoch  than  with  the  Peorian. 

In  attempting  to  arrive  at  a  definite  conclusion  as  to  the 
Peorian  interglacial  epoch  the  following  lines  of  investigation  have 
been  undertaken:  (i)  the  amount  of  erosion  shown  by  the  two  last 
drift-sheets,  (2)  the  degree  of  leaching  and  oxidation  of  the 
Wisconsin  and  lowan  till-sheets,  (3)  the  amount  of  erosion  affected 
on  the  lowan  drift  before  the  advance  of  the  Wisconsin,  (4)  the 
outwash  products  of  the  Wisconsin  border  and  their  state  of 
preservation  as  compared  with  similar  deposits  of  the  lowan  and, 
(5)  the  study  of  the  interglacial  deposits. 

One  of  the  evidences  as  to  whether  little  or  much  time  has 
elapsed  since  the  deposition  of  a  drift-sheet,  is  the  amount  of 
erosion  that  has  been  accomplished  since  the  deposition  of  the 
drift.  The  Wisconsin  drift  area  may  be  divided  into  two  distinct 
regions:  (i)  the  terminal  moraine  area  and,  (2)  the  interior  or 
plain-phase  area.  Since  the  Wisconsin  was  a  vigorous  ice-sheet  it 
built  along  its  margin  a  prominent  terminal  moraine.  This 
moraine  is  more  conspicuous  for  marked  relief  in  some  places  than 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  61 

others.  This  terminal  area  may  be  characterized  as  a  surface 
broken  by  knobs  and  depressions  with  no  apparent  attempt  at  any 
order  of  assemblage.  Many  of  the  depressions  are  large,  deep,  and 
without  outlets.  In  these  deep  kettles  are  to  be  found  Iowa's  largest 
lakes.  So  recent  has  been  the  retreat  of  this  ice-sheet  that  the 
carving  effect  of  running  water  has  in  no  way  changed  the  contour 
of  these  hills. 

The  interior  plain-phase  is  characterized  by  a  level  surface 
which  is  broken  by  gentle  undulating  swells  and  compensating 
convexities,  which  give  rise  to  numerous,  shallow,  undrained  saucer- 
like  depressions. 

So  slight  is  the  surface  relief  that  drainage  is  difficult.  In  this 
area  the  only  evidence  of  erosion  is  to  be  found  along  some  of  the 
major  streams,  which  are  still  flowing  in  courses  they  occupied 
before  the  advance  of  the  Wisconsin  ice-sheet.  All  the  larger 
valleys  have  the  appearance  of  immaturity.  The  only  exceptional 
phase  of  topography  found  within  the  plain-phase  is  the  prominent 
hills,  sometimes  solitary,  sometimes  grouped  in  irregular  clusters, 
which  seem  to  rise  out  of  the  level  plain.  At  first,  these  hills  give 
the  appearance  of  hills  that  have  been  formed  by  erosional  agents, 
but  upon  closer  examination  they  are  observed  to  be  constructional 
and  of  glacial  origin.  They  represent  the  halting  attitude  of  the 
ice  edge  in  its  northward  recession.  Excellent  examples  of  these 
morainic  hills  may  be  seen  in  Hamilton  and  Wright  counties.  The 
numerous  small  ponds  and  marshes,  the  larger  lakes  associated  with 
the  terminal  moraine  hills,  the  undissected  surface  all  testify  to  a 
surface  much  the  same  as  it  was  after  the  retreat  of  the  Wisconsin 
ice-sheet. 

In  passing  from  the  Wisconsin  border  to  the  lowan  drift  but 
little  disparity  in  topographic  evidence  is  noticeable  (see  Plate  VI.). 
Much  of  the  same  undulatory  surface  effects  are  present  only 
slightly  exaggerated.  Drainage  lines  are  a  little  more  pronounced, 
there  being  a  tendency  in  places  to  take  on  the  dendritic  pattern. 
The  relief  in  some  portions  of  the  lowan  plain  is  as  great  as  50 
feet.  The  surface  of  the  lowan,  in  many  places,  resembles  a  pre- 
glacial  topography  that  has  been  softened  by  a  thin  mantling  of 
drift. 

This  is  quite  noticeable  in  passing  from  some  of  the  larger 
streams  that  head  in  the  Wisconsin  drift  and  continue  their  courses 
across  the  lowan.  In  the  lowan  area  the  valleys  are  large  and  out 
of  all  proportion  to  the  sizes  of  the  streams  found  in  them.  Upon 
closer  examination  it  is  discovered  that  these  channels  are  pre- 
lowan  in  age,  this  fact  being  shown  by  the  superposition  of  lowan 
drift  over  Buchanan  gravels  in  valley  bottoms.  In  many  instances 
so  little  erosion  has  been  accomplished  by  the  streams  since  the 
deposition  of  the  lowan  drift  in  these  valley  bottoms  that  the 
streams  have  failed  to  cut  through  the  thin  veneer.  The  numerous 
small  ponds  and  marshes  found  upon  the  gentle  slopes  of  runs  and 
draws,  and  in  the  valley  bottoms  and  on  the  crests  of  gentle  swells, 
the  small  amount  of  dissection  of  the  drift  plain  indicate  clearly 
no  great  period  of  erosion  between  the  deposition  of  the  lowan 
drift  and  the  advance  of  the  Wisconsin  ice. 

While  it  is  not  possible  always  to  distinguish  the  different 
drift-sheets  by  their  color  or  lithological  composition,  it  is  .gener- 
ally more  possible  to  tell  the  Wisconsin  from  the  other  till-sheets 
by  its  color.  Except  in  restricted  areas,  where  the  Wisconsin  is 


62  OXIDATION  AND  LEACHING  OF  THE  DRIFT 

more  or  less  sandy,  the  drift  is  of  a  light  yellow  color,  while  the 
older  drifts,  due  to  a  more  advanced  stage  of  weathering,  are  more 
of  a  brownish  yellow  to  a  reddish  brown  color.  Its  freshness  is 
further  shown  by  the  predominance  of  limestone  pebbles  and 
bowlders,  many  of  the  latter  showing  striae  as  fresh  as  if  deposited 
but  yesterday.  Granite  bowlders  are  present  and  differ  from  those 
of  the  lowan  area  in  size  and  general  color,  the  color  of  the 
Wisconsin  bowlders  being  prevailingly  darker  than  those  of  the 
lowan  area.  Very  little  difference  in  the  degree  of  weathering  of 
the  Wisconsin  and  lowan  bowlders  can  be  detected,  the  bowlders  of 
the  lowan  showing  as  fresh  a  surface  as  do  those  of  the  Wisconsin. 

The  difference  in  age  of  the  lowan  and  Wisconsin  drift-sheets 
is  shown  best  by  the  degree  of  weathering.  It  will  be  seen  that  the 
depth  of  oxidation,  figure  (i)  is  greater  for  the  lowan.  To  deter- 
mine the  depth  of  leaching,  auger  borings  were  made  on  the  two 
drifts,  the  locations  for  the  borings  being  chosen  where  topographic 
conditions  were  similar  for  both  drifts.  The  average  depth  of 
leaching  shown  on  the  Wisconsin  was  1.5  feet,  while  the  lowan 
showed  a  depth  of  leaching  of  3.9  feet. 

A  study  of  the  morainal  border  of  the  Wisconsin  drift  where  it 
is  in  proximity  to  the  lowan  drift  for  outwash  plain  evidence,  failed 
to  reveal  any  worthy  of  note.  Locally  there  are  subdued 
phases,  but  topographically  they  are  of  little  importance.  A  type 
section  of  such  outwash  plains  is  found  in  sections  5,  8  and  9  of 
Reeve  township,  Franklin  county. 

Feet.  Inches. 

1.  Peat,  muck  and  black  soil,  highly  fossiliferous 2-4 

2.  Clay,  fine  textured  and  white  in  color 6-12 

3.  Gravel,  stratified,  containing  pebbles  which  vary  in 

size  from  one-fourth  to  one-half  inches 2-4 

4.  Sand   and  clay,   greenish   in  color,   fine   grained   and 

uniform   in   texture 2 

5.  White  sand,  even  grained  and  pebbleless 2 

During  the  time  that  the  Wisconsin  ice  front  occupied  a 
position  to  the  west  of  the  above  outwash  plain,  an  extensive  lake 
was  formed  immediately  in  front  of  the  ice-edge  into  which  was 
washed  the  fine  rock  flour,  sand  and  gravel.  The  most  important 
outwash  deposits  found  along  the  eastern  border  of  the  Wisconsin 
terminal  moraine  are  kames,  kame-like  eskers  and  the  valley  trains. 
All  the  larger  streams  which  issue  from  the  morainal  border  are 
fringed  with  more  or  less  continuous  gravel  deposits  which  are 
usually  in  the  form  of  terraces  in  the  larger  valleys  of  the  lowan 
drift  area. 

In  some  cases  these  deposits  may  be  traced  for  great  distances 
beyond  the  morainal  border,  and  not  infrequently,  they  are  found 
extending  back  across  the  terminal  moraine  onto  the  Wisconsin 
drift.  Some  of  the  more  important  deposits  are  to  be  found  near 
Gifford,  Hardin  county,  where  the  South  Fork  of  the  Iowa  river 
joins  the  parent  stream;  at  Sheffield,  along  Bailey's  creek,  Franklin 
county,  and  at  Thornton,  on  Beaver's  creek,  Cerro  Gordo  county. 
The  material  is  largely  sand  and  gravel,  and  varies  greatly  from 
place  to  place.  The  gravels  are  largely  composed  of  pebbles  of 
limestone,  granite,  quartzite,  greenstones,  and  quartz.  As  a  whole 


SOME  PHASES  OF  THE  PLEISTOCENE  O'F  IOWA 


63 


the   gravels  are   fresh  in  appearance,  except  where   they  are  poorly 
drained.     In  such  positions  the  gravel  is  highly  iron  stained. 

Kame-like  eskers  were  seen  in  the  valley  of  Elk  Creek,  sections 
21,  22  and  23,  Brookfield  township,  Worth  county,  and  in  section  24, 
Green  township,  Cerro  Gordo  county. 

The  lowan  gravels  when  compared  with  the  Wisconsin  gravels 
show  a  higher  state  of  weathering,  though  not  nearly  so  great  as 
the  difference  between  the  Kansan  and  the  lowan.  This  would 
seem  to  clearly  indicate  that  the  time  between  the  deposition  of  the 
lowan  gravels  and  the  coming  of  the  Wisconsin  ice,  was  a  shorter 
interglacial  epoch  than  any  of  the  former  interglacial  epochs. 

The  shorter  time  is  further  emphasized  by  the  degree  of  erosion 
shown  by  the  lowan  drift  when  contrasted  with  the  erosion  of  the 
Wisconsin.  That  little  erosion  has  taken  place  in  the  valleys  of  the 
lowan,  bordering  the  Wisconsin,  is  shown  by  the  fact,  that  in  no 
instance  have  valleys  of  any  depth  been  excavated  in  the  lowan 
drift.  On  the  other  hand,  it  is  found  that  where  streams  cross 
from  the  Wisconsin  onto  the  lowan,  their  channels  on  the  latter 
drift  are  for  the  most  part  in  bed-rock,  and  are  out  of  all  propor- 
tion to  the  size  of  the  streams  found  in  them.  It  can  be  demon- 
strated clearly  that  the  major  streams  are  flowing  in  valleys  that 
are  pre-Iowan.  One  of  the  best  examples  is  that  of  Lime  creek.  In 
the  S.E.  1A  Sect.  35  and  S.  l/2  of  Sect.  36,  Fertile  township,  Worth 
county,  where  the  river  flows  along  the  northern  margin  of  the 
Wisconsin  drift,  there  is  found  the  following  interesting  relations 
of  the  drift-sheets  to  the  valley. 


Figure   7. 

Type  section  of  Lime  creek  valley  east  of  Fertile. 

To  the  north  of  the  river  is  the  broad  flood-plain  of  the  river 
with  its  distinct  terraces  covered  with  lowan  drift.  Here  the 
Buchanan  gravels  can  be  seen,  covered  with  lowan  bowlders.  To 
the  south  of  the  river  and  immediately  bordering  it  may  be  seen 
the  steep  bluff  reaching  to  a  height  of  90  feet.  This  bluff  is  com- 
posed of  Kansan  drift  beneath,  and  Wisconsin  drift  above.  A 
section  of  this  bluff  was  taken  which  shows  the  following  inter- 
esting facts. 


64     RELATION  OF  THE  WISCONSIN  DRIFT  TO  THE  1OWAN 

Feet. 

1.  Sand    and    gravel,    largely    sand    in    the    upper   part, 

and  yellowish  brown  color 18 

2.  Clay,  yellowish  gray,  highly  stained  with  iron  along 

the  joints  and  smaller  fissures 2 

3.  Clay,    grayish    yellow,    highly   calcareous;    limestone 

pebbles    numerous , 22 

4.  Clay,  bluish,  compact,  highly  calcareous 40 

5.  Soil    and   muck   on    a   bluish,    compact   jointed   clay; 

contains  pieces  of  wood  and  fossil  shells 2 

This  would  seem  to  indicate  clearly  that  the  channel  of  Lime 
creek  is  pre-Iowan  in  age  and  probably  of  post-Kansan  origin. 
Many  other  streams  in  the  lowan  area  bordering  the  Wisconsin, 
show  this  same  relationship  to  the  lowan  drift. 

A  careful  and  detailed  investigation  was  made  along  the  east- 
ern margin  of  the  Wisconsin  drift,  where  this  drift  is  thought  to 
overlap  the  lowan,  to  see  if  it  were  possible  to  find  any  evidence  of 
an  overlap  and  to  discover,  if  possible,  evidence  of  interglacial 
deposits.  This  border  extends  from  the  northern  boundary  line  of 
Iowa,  in  Worth  county,  to  Eldora,  in  Hardin  county.  Examinations 
of  well  logs,  sections  of  the  drift,  and  a  new  coal  shaft,  failed  to 
reveal  the  presence  of  anything  that  could  be  positively  called 
lowan  drift,  immediately  underlying  the  Wisconsin,  along  this 
border.  There  were  no  evidences  found  of  interglacial  deposits 
that  could  be  said  to  be  Peorian  in  age.  A  further  investigation  of 
the  Wisconsin  drift  to  the  west  was  made  to  determine,  if  possible, 
whether  the  lowan  drift  extended  westward  beneath  the  Wisconsin 
drift.  Sections  examined  in  Hardin,  Hamilton,  Boone  and  Webster 
counties  failed  to  show  any  positive  evidence  of  lowan  drift.  The 
result  of  this  investigation  has  led  to  the  'following  conclusions: 
(i)  if  the  Peorian  was  of  sufficient  length  to  permit  of  the  develop- 
ment of  a  soil  and  forest  zone,  the  vigor  and  strength  of  the 
Wisconsin  ice,  when  it  overrode  the  lowan  area,  destroyed  all  evi- 
dence of  such  deposits;  (2)  If  the  Wisconsin  overlapped  the  lowan 
for  any  great  distance,  all  such  evidence  has  been  obliterated.  This 
may  be  due  to  the  fact  that  the  lowan,  being  a  thin  drift-sheet, 
may  have  been  incorporated  with  the  Wisconsin  drift  and  hence 
has  lost  its  identity;  (3)  the  only  deposit  that  is  so  far  recognizable 
as  Peorian  in  age,  is  the  loess. 

The  result  of  the  investigation  has  led  to  the  following  judg- 
ments regarding  the  Peorian  Interglacial  Epoch; 

I.  Geologically,  the  Peorian  was  the  shortest  of  the-  inter- 
glacial epochs.  The  evidence  which  seems  to  justify  such  a  conclu- 
sion is,  (i)  the  small  amount  of  erosion  of  the  lowan  drift  between 
its  deposition  and  the  advance  of  the  Wisconsin  ice,  (2)  the  great 
similarity  of  topographic  evidence  between  the  lowan  and  the 
Wisconsin,  (3)  the  small  degree  of  difference  shown  in  the  state  of 
weathering  of  the  two  drift-sheets,  (4)  the  depth  of  leaching  of 
the  two  drifts  is  such  as  to  suggest  that  the  two  drifts  are  not  con- 


SOME  PHASES  OF  THE  PLEISTOCENE  OF  IOWA  65 

temporaneous,  and  a  comparison  of  the  weathered  state  of  the 
Wisconsin  and  lowan  gravels  shows  the  Wisconsin  gravels  to  be 
younger  than  the  lowan  gravels,  but  of  no  such  great  difference  as 
is  shown  between  the  weathered  state  of  the  Kansan  and  lowan 
gravels,  (5)  the  time  may  be  largely  represented  by  the  loess 
deposition  and  the  small  amount  of  oxidation  and  leaching  that  has 
taken  place  in  the  loess. 

II.  The  Peorian  interglacial  epoch  is  best  represented  by  the 
loess  deposits.  Evidence  seems  to  justify  the  assumption  that  the 
Peorian  was  a  period  during  which  conditions  were  favorable  for 
the  making  of  thick  deposits  of  loess.  That  the  loess  is  of  Peorian 
age  has  been  shown  by,  (i)  its  stratigraphic  relations  to  the  lowan 
and  Wisconsin  drift-sheets,  (2)  by  the  fact  that  where  it  is  found 
to  occupy  a  position  between  the  Kansan  and  Wisconsin  drift- 
sheets,  it  shows  a  sharp  line  of  demarcation  from  the  Kansan  drift, 
often  resting  on  Kansan  gumbotil,  and  is  found  calcareous  and 
fossiliferous  from  base  to  top.  This  would  seem  to  warrant  the 
assumption  that  the  loess  must  have  been  deposited  shortly  after 
the  withdrawal  of  the  lowan  ice  and  sufficiently  rapid  not  to 
permit  leaching  and  oxidation  to  keep  pace  with  the  accumulation, 
and  that  the  Wisconsin  ice  must  have  advanced  shortly  after  the 
deposition  of  the  loess,  as  the  zone  of  leaching  and  oxidation  be- 
neath the  Wisconsin  drift  is  very  shallow. 


BIBLIOGRAPHY. 

T.  C.   Chamberlin.     Glacial   and  interglacial   beds  near  Toronto. 
Jour,  of  Geology,  Vol.  9,   1901,  p.   285. 


' 


r 


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